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Second Meeting: 5th June, 1907.
Professor H. B. Kirk, President, in the chair.
New Members.—Mr. H. Vickerman and Mr. A. G. Stuckey.
Papers.—1. “A Description of Two New and Improved Forms of the Almucantar,” by C. W. Adams.
The following remarks apply chiefly to the method of flotation: This almucantar floats on mercury, which is in a circular cast-iron trough resting on a circular concrete wall 4 ft. high and 6 in. thick. The mean diameter of the circular trough, and of the wall which supports it, is 6 ft. The cross-section of the trough is a semicircle, diameter 6 in., and is capable of floating a weight of 14 cwt., or, say, 12 cwt. without any fear of the mercury spilling over. (By increasing the diameter of the circular trough to 9 ft., and making it of a similar cross-section and 1 ft. wide, it would float a weight of over 4 tons.) The telescope is suspended from a domeshaped framework, the observer being free to move about inside the circular wall. The azimuth circle may be engraved on the inner or outer upper edge of the circular trough containing the mercury, the zero being placed wherever the observer prefers. The divisions are read by four micrometers, as verniers are inadmissible on account of friction. These micrometers could be read by one or more assistants outside the concrete wall, if necessary. With four assistants a great many more observations could be made than when the observer had to read all the microscopes himself. The clamping should be done by electricity, so as to avoid disturbance of the floating instrument; also, the instrument should not be turned round by hand directly, but by means of apparatus attached to a vertical pillar under the centre of the instrument. Only a few pounds of mercury is required, as, if the inside of the trough and the bottom of the framework are turned in a lathe, so as to accurately fit each other, there will merely be a thin film of mercury between the two.
The pedestal of this almucantar is an ordinary cast-iron gaspipe, about 9 in. in diameter externally, and 6 ft. long, sunk 3 ft. in the ground. A cast-iron cylindrical cap fits on this, 12 in. in height and 12 in. in external diameter, with a hemispherical cup 10 in. diameter, turned out of the top, as a reservoir for the mercury. This cap is furnished with four adjusting-screws, pressing against the internal gaspipe, by which the top of the cap can be fixed in a horizontal plane. The platform on top is
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attached to a hemisphere, which fits into the hemispherical cup containing the mercury, a thin film of which supports the platform. The mercury can support a weight of 128 lb., or we may say 100 lb. without any fear of the mercury spilling over. The platform has a heavy cylindrical attachment which brings the centre of gravity below the bowl containing the mercury. The azimuth circle should be engraved on the upper edge of the hemispherical bowl, and the divisions read by a micrometer attached to the frame or platform on top. A portable almucantar should not be used for general azimuth - work, but the azimuth circle is required as a setting - circle when observing for time or latitude. An ordinary theodolite can be set up on the platform, or a special instrument constructed. In a small model that I constructed, in which the hemisphere and the bowl for it to float in were turned out of wood, the motion was beautifully smooth; the least touch with the little finger would suffice to turn the instrument round, and, if set spinning, it would make a good many revolutions before it came to rest.
2. “A New Method for the Preparation of Ketones,” by Professor T. H. Easterfield.
Exhibits.—1. Mr. G. V. Hudson exhibited the following:—
(a) Three parts of a work entitled “Australian Lepidoptera and their Transformation,” by A. W. Scott, with hand-coloured plates; published in 1864.
(b.) A series of Dodonidia helmsii, a rare New Zealand butterfly, taken at Silverstream in February, 1907.
(c.) Two female specimens of Titanornis sisyrota, a gigantic tineid moth not seen alive since 1886, and perhaps now extinct—one taken by Mr. Clement W. Lee, at Otaki, in March, 1886; the other taken in Nelson many years ago. The male is unknown.
(d.) Male and female specimens of Macropathus maximus, a gigantic tree-weta, captured at Kaitoke under the bark of dead birches on the 31st December, 1906; originally described by Sir Walter Buller from a single specimen.