543
(10)
Japan. Hongkong itself occupies a position which is comparatively exempt from typhoons, the great majority of these storms passing either to the east or south of the island. As is shown in an able monograph lately published by the Director of the Zi Ka Wei observatory, near Shanghai, out of thirteen typhoons which traversed the South China sea last year, two only passed at all near to Hongkong, and of these the centre-tracks were at a sufficiently safe distance. Nevertheless, it is hardly possible to overstate the value of Manila as a warning station for vessels about to leave Hongkong for southern, eastern or northern ports, or vessels approaching it from those places. Means should therefore be provided for enabling the Director of the Hongkong Observatory to be placed, whenever necessary, in prompt communication by telegraph with Manila, Amoy, Shanghai, Saigon and Singapore, as well as with the south of Japan. A system of daily telegraphic weather exchanges with the chief ports should also be organized as soon as possible. For these purposes, it will be necessary to connect the Observatory with the existing telegraph line which crosses the harbour from Kau-lung Dock to Whitfield Police Station. The Observatory may thus be made to fulfil the useful purpose of a Weather Intelligence Office in times of danger for the whole neighbouring region; while, from the daily exchanges, ships' logs, and trustworthy private observations, a large body of facts relating to typhoons and the monsoons may be gradually amassed.
It is most unfortunate that the south part of Formosa is not as yet provided with telegraphic means of communication. This is a cardinal point in the chain of surrounding stations, and, until it is brought into telegraphic connexion with the rest, our system of weather intelligence cannot be made as perfect as might be desired. The exclusion of Hainan in this respect is also to be regretted, For purposes of warning to vessels in Hongkong harbour, a signal-mast should be erected near the Time-Ball at Kau-lung, and a code of signals established and given the fullest publication. These signals might be repeated on the existing mast at the Harbour Office.
When the scientific establishment at Kau-lung has been fairly started, it will probably be considered needless to keep up all of the meteorological stations now existing in different parts of the Colony. I certainly think that the stations at the Harbour Office, Stone Cutters' Island and the Hospital might very well be abolished. But I would recommend that those at Victoria Peak and Cape d'Aguilar be retained, as they are points at which observations, especially those of the barometer and the wind, will always be of value; and I suggest that both places be supplied with an anemometer, in order that the wind may be observed more accurately than is possible at present, care being taken to get instruments of superior strength.*
*This however, so far as it concerns Cape d'Aguilar, must depend upon whether good observations of the wind can be obtained at or near to the light-house, a point which may be easily ascertained.
(11)
III Terrestrial Magnetism.
Although the character of the rocks and soil of Hongkong and Kau-lung is not the most favourable that could be chosen for magnetic research, yet the position of the Colony on the magnetic chart, and with respect to other places where observatories are already established, leaves no room to doubt that well-conducted observations of this class will be of great value to the science. These will comprise observations for determining the Absolute Values of the elements of the Earth's magnetic force,- namely, its Declination, Inclination and Intensity--as well as those for ascertaining the periodic, secular and irregular Variations which the elements undergo, and the laws of which still await complete theoretical explanation. The former class of determinations, i.e., those of Absolute values-are pretty certain to be more or less prejudicially affected by local attraction proceeding from the granitic rocks and soil; but the Variations, which form by far the more important object of research, can be deduced just as well in the presence as in the absence of local attraction.
The instruments with which Dr. De La Rue proposes to equip the magnetic branch are,
A set of photographic self-registering Magnetic instruments, of the Kew pattern, with accessories, &c.;
A Unifilar Magnetometer;
A Dip-Circle, with four needles;
all of which, as well as the Meteorological instruments, will be verified at Kew before they are sent out. Their total cost is estimated at £424.
The Photographic instruments will comprise three Magnetometers, for continuous registration of the changes in the declination and the horizontal and vertical forces by means of a central recording apparatus, driven by clockwork and carrying the photographic papers--the whole constituting, with certain accessories, a complete Magnetograph. They will exhibit the periodic variations, as well as those mysterious phenomena of simultaneous disturbance extending over the entire earth's surface, and called magnetic storms, which are amongst the most extraordinary in the whole range of physics.
The magnet of the Declination magnetometer is placed in the magnetic meridian; that for measuring variations of the Horizontal force is compelled by torsion to take a position transverse to the meridian; the third, for measuring variations of Vertical force, is balanced on knife-edges.
The Unifilar Magnetometer is used for ascertaining the absolute value of the horizontal component of the total force in the direction of the dip, by observations of deflection and vibration. It is also used for determining the absolute declination.
The Dip-Circle affords measures of the magnetic inclination, or "dip," and can be used under certain circumstances for measuring variations of the total force.
The chief magnetic building, for the differential instruments, should be a basement or vault, almost wholly underground, and contain an instrument-chamber and a photographic laboratory. I recommend about 22 feet by 20 feet and 12 feet by 10 feet as suitable dimensions for those rooms, and the building should be laid out with the long side of the instrument-room inclined 15 degrees to the west of the magnetic north, the laboratory being at the northern end.
The annexed small drawing will give an idea of the character of the building which I propose, and of the positions of the instruments. It shows that the actual chamber for the magnetograph has an arched roof, and is wholly enclosed within a similar building, the walls and roofs of the two being separated by a space of two feet. The floor of the chamber is 15 feet below the surface of the ground, and the highest point of the external arch is 21 feet above the floor. Covering this arch, there will be (1) inch asphalte, (2) six inches of fine concrete, (3) two feet of earth; the surface being finally turfed. Small relieving arches will need to be built at intervals between the side walls of the outer and inner chambers, in order to meet the thrust upon the inner walls. The main chamber will be quite dark, but a small amount of yellow light will be admitted to the laboratory.
Although the vault form of construction is the best for differential magnetic observations, since it secures the great desideratum of an equable temperature, there are obvious complications and difficulties connected with it. Thorough drainage must be carefully provided, in order to keep it dry; and there must be arrangements for carrying off the heat and smoke of lamps. Ventilation also presents a grave difficulty, especially in a climate so hot and damp as that of Hongkong is during several months of the year. It is evident that, if warm air laden with moisture be admitted to an underground chamber which is appreciably cooler, it will produce a constant state of saturation, and be continually depositing its moisture on the delicate instruments and apparatus. A long underground air-flue, connected with vertical shafts, must therefore be provided, in order that the incoming air may be cooled to the temperature of the vault, as nearly as possible, before reaching it. These devices are of course expensive, but it is better to put up with the cost than to face the alternative of a building above ground, in which the great variations of temperature would be fatal to satisfactory observation.
For the above and other essential details, Mr. BOWDLER's past experience in designing and erecting the excellent Magnetic Observatory at Mauritius will prove of the utmost service in the present case. Mr. BOWDLER has, indeed, been good enough to prepare a detailed drawing after the pattern of the Mauritius building, and although I propose, for the sake of economy, to depart in some important respects from the plan there carried out, his drawing furnishes much practical and useful information, applicable to all works of this kind. It has been of great service to me in preparing the accompanying design.
It remains to consider the material which shall be used for the magnetic building, and which, as needs hardly be stated, must be practically free from iron. Unfortunately, the granite of this region is out of the question, on account of the large percentage of protoxide of iron which it contains. For the same reason we must condemn the concrete that is in common use in Hongkong, since its main ingredient...
543
(10)
Japan. Hongkong itself occupies a position which is comparatively exempt from typhoons, the great majority of these storms passing either to the cast or south of the island. As is shown in an able monograph lately published by the Director of the Zi Ka Wei observatory, near Shanghai, out of thirteen typhoons which traversed the South China sea last year, two only passed at all near to Hong- kong, and of these the centre-tracks were at a sufficiently safe distance. Nevertheless, it is hardly possible to overstate the value of Manila as a warning station for vessels about to leave Hongkong for southern, eastern or northern ports, or vessels approaching it from those places. Means should there- fore be provided for enabling the Director of the Hongkong Observatory to be placed, whenever ne- cessary, in prompt communication by telegraph with Manila, Amoy, Shanghai, Saigon and Singapore, as well as with the south of Japan. A system of daily telegraphic weather exchanges with the chief ports should also be organized as soon as possible. For these purposes, it will be neces- sury to connect the Observatory with the existing telegraph line which crosses the harbour from Kau-lung Dock to Whitfield Police Station. The Observatory may thus be made to fulfil the useful purpose of a Weather Intelligence Office in times of danger for the whole neighbouring region; while, from the daily exchanges, ships' logs, and trustworthy private observations, a large body of facts relating to typhoons and the monsoons may be gradually amassed.
It is most unfortunate that the south part of Formosa is not as yet provided with telegraphic means of communication. This is a cardinal point in the chain of surrounding stations, and, until it is brought into telegraphic connexion with the rest, our system of weather intelligence cannot be made as perfect as might be desired. The exclusion of Hainan in this respect is also to be regretted, For purposes of warning to vessels in Hongkong harbour, a signal-mast should be erected near the Time-Ball at Kau-lung, and a code of signals established and given the fullest publication. These signals might be repeated on the existing mast at the Harbour Office.
When the scientific establishment at Kau-Inng has been fairly started, it will probably be considered needless to keep up all of the meteorological stations now existing in different parts of the Colony. I certainly think that the stations at the Harbour Office, Stone Cutters' Island and the Hospital might very well be abolished. But I would recommend that those at Victoria Peak and Cape d'Aguilar be retained, as they are points at which observations, especially those of the barometer and the wind, will always be of value; and I suggest that both places be supplied with an anemometer, in order that the wind may be observed more accurately than is possible at present, care being taken to get instruments of superior strength.
III Terrestrial Magnetism.
Although the character of the rocks and soil of Hongkong and Kau-lung is not the most favourable that could be chosen for magnetic research, yet the position of the Colony on the magnetic chart, and with respect to other places where observatories are already established, leaves no room to doubt that well-conducted observations of this class will be of great value to the science. These will com- prise observations for determining the Absolute Values of the elements of the Earth's magnetic force,- namely, its Declination, Inclination and Intensity--as well as those for ascertaining the periodic, secular and irregular Variations which the elements undergo, and the laws of which still await complete theoretical explanation. The former class of determinations, i. e., those of Absolute values-are pretty certain to be more or less prejudicially affected by local attraction proceeding from the granitic rocks and soil; but the Variations, which form by far the more important object of research, can be deduced just as well in the presence as in the absence of local attraction.
The instruments with which Dr. De La Rue proposes to equip the magnetic branch are,
A set of photographic self-registering Magnetic instruments, of the Kew pattern, with
accessories, &c. ;
A Unifilar Magnetometer;
A Dip-Circle, with four needles;
all of which, as well as the Meteorological instruments, will be verified at Kew before they are sent out. Their total cost is estimated at £424.
*This however, so far as it concerns Cape d'Aguilar, must depend upon whether good observations of the wind can be obtained at or near to the light-house, a point which may be easily ascertained,
*
( 11 )
The Photographic instruments will comprise three Magnetometers, for continuous registration of the changes in the declination and the horizontal and vertical forces by means of a central recording apparatus, driven by clockwork and carrying the photographic papers--the whole constituting, with certain accessories, a complete Magnetograph. They will exhibit the periodic variations, as well as those mysterious phenomena of simultaneous disturbance extending over the entire earth's surface, and called magnetic storms, which are amongst the most extraordinary in the whole range of physics.
The magnet of the Declination magnetometer is placed in the magnetic meridian; that for measuring variations of the Horizontal force is compelled by torsion to take a position transverse to the meridian; the third, for measuring variations of Vertical force, is balanced on knife-edges.
The Unifilar Magnetometer is used for ascertaining the absolute value of the horizontal component of the total force in the direction of the dip, by observations of deflection and vibration. It is also used for determining the absolute declination.
The Dip-Circle affords measures of the magnetic inclination, or "dip," and can be used under certain circumstances for measuring variations of the total force.
The chief magnetic building, for the differential instruments, should be a basement or vault, almost wholly underground, and contain an instrument-chamber and a photographic laboratory. I recommend about 22 feet by 20 feet and 12 feet by 10 feet as suitable dimensions for those rooms, and the build- ing should be laid out with the long side of the instrument-room inclined 15 degrees to the west of the magnetic north, the laboratory being at the northern end.
The annexed small drawing will give an idea of the character of the building which I
propose, and of the positions of the instruments. It shows that the actual chamber for the magnetograph has an arched roof, and is wholly inclosed within a similar building, the walls and roofs of the two being separated by a space of two feet. The floor of the chamber is 15 feet below the surface of the ground, and the highest point of the external arch is 21 feet above the floor. Covering this arch, there will be (1) inch asphalte, (2) six inches of fine concrete, (3) two feet of earth; the surface being finally turfed. Small relieving arches will need to be built at intervals between the side walls of the outer and inner chambers, in order to meet the thrust upon the inner walls. The main chamber will be quite dark, but a small amount of yellow light will be admitted to the laboratory.
Although the vault form of construction is the best for differential magnetic observations, since it secures the great desideratum of an equable temperature, there are obvious complications and diffi- culties connected with it. Thorough drainage must be carefully provided, in order to keep it dry; and there must be arrangements for carrying off the heat and smoke of lamps. Ventilation also presents a grave difficulty, especially in a climate so hot and damp as that of Hongkong is during several months of the year. It is evident that, if warm air laden with moisture be admitted to an underground chamber which is appreciably cooler, it will produce a constant state of saturation, and be continually depositing its moisture on the delicate instruments and apparatus. A long underground air-flue, connected with vertical shafts, must therefore be provided, in order that the incoming may be cooled to the temperature of the vault, as nearly as possible, before reaching it. These devices are of course expensive, but it is better to put up with the cost than to face the alternative of a building above ground, in which the great variations of temperature would be fatal to satisfactory observation.
air
For the above and other essential details, Mr. BOWDLER's past experience in designing and erecting the excellent Magnetic Observatory at Mauritius will prove of the utmost service in the present case. Mr. BOWDLER has, indeed, been good enough to prepare a detailed drawing after the pattern of the Mauritius building, and although I propose, for the sake of economy, to depart in some important respects from the plan there carried out, his drawing furnishes much practical and useful information, applicable to all works of this kind. It has been of great service to me in preparing the accompanying design.
It remains to consider the material which shall be used for the magnetic building, and which, as needs hardly be stated, must be practically free from iron. Unfortunately, the granite of this region is out of the question, on account of the large percentage of protoxide of iron which it contains. For the same reason we must condemn the concrete that is in common use in Hongkong, since its main ingre-
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