560 



Proceedings. 



Second Meeting : Uh 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 dome- 

 shaped framework, the observer being free to move about inside the cir- 

 cular 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 



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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 dis- 

 turbance 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 

 '.) 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 ex- 

 ternal 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 



