176 Proceedings of the 



assembled members. The philosophy of flame, its extinction, and 

 the effect of non-conductors, were first distinctly laid down ; and 

 then the powers of tiie apparatus already described, practically 

 shewn. All the experiments that could be repeated in a lecture- 

 room were made ; and, in place of those with double hedges of 

 flame, the fireman, clothed and guarded, was exposed to a large 

 and powerful flame from the mouth of a condensed gas vessel. 

 The specimens of asbestos cloth and clothing, laid by M. Aldini 

 upon the lecture-table, were upon so large a scale as to surpass, 

 probably, all that had ever been seen before them. 



In the Library, Captain Grover explained a small pocket azimuth 

 and altitude instrument of Captain Rater's invention ; and, as 

 Captain Kater has not as yet given a detailed description of this 

 exceedingly useful instrument, the following brief account may not 

 be unacceptable. 



The great advantages it possesses, are — extreme portability ; the 

 ease and accuracy with which it can be used ; and its cheapness. 



A circle, three inches in diameter, is fixed to a hollow cone, which 

 moves upon a solid axis, and the whole is supported by a tripod 

 stand, into which this axis screws. At the back of the circle is fixed 

 a spirit level. A telescope, magnifying about eight times, to which 

 are fixed two opposite verniers, moves upon the circle ; there is, 

 also, a tangent-screw for slow motion. A ball and socket is screwed 

 into the back of the instrument, which serves as a counterpoise 

 when vertical angles are taken. 



In the focus of the telescope are placed one vertical and three 

 horizontal spiders' threads, which are illuminated by a very inge- 

 niously contrived reflector, forming a portion of a hollow cone, 

 silvered inside, which fits upon the object end of the telescope. 



The motion in azimuth is given by two projecting pieces attached 

 to a tube, which fits rather tightly on the conical axis ; these pieces 

 serve also, by being brought in a line with one of the radii of the 

 tripod-stand, when the telescope is directed to a star, to turn the 

 instrument 180^ in azimuth, so as to bring the star into the field of 

 view when the face of the circle is changed from left to right. 



To use this instrument, it must be carefully levelled, and the 

 telescope being directed to a star, or other object, so that it appears 

 upon the horizontal wire, and upon or very near the vertical wire, 

 the verniers read off the apparent elevation to minutes. The circle 

 is then turned half-round in azimuth, and the angle being read off 

 by the two verniers, we have the altitude deduced from the mean 

 of four readings. 



