[ i6 ] 



is perforated with a fmall hole, and in this is inferted a convex 

 lens ; the plate and the pillar are perforated alfo in the diredion 

 of the axis ; the perforation in the pillar near the back part is 

 three inches in diafneter ; in this is inferted a tube carrying ano- 

 ther larger convex lens ; to this tube is attached the lantern, in 

 which the flame of the candle is kept always oppofite the axis of 

 the tube by means of a fpring focket. 



The rays of light iffuing from the candle are by thefe lenfcs 

 brought to a focus immediately beyond the fmall lens inferted in 

 the pivot, and diverging from thence, within the conical axis, 

 are intercepted at the fquare box in the centre by a diagonal 

 plate of filvcred brafs, which rcfledls the light down to the 

 wires ; this plate is perforated with an elliptical hole, to let the 

 cone of rays from the objedl glafs pafs through undiminifhed. 

 See Fig. IV. 



To temper this light in proportion to the ftar obferved, 

 there is a green glafs increafing gradually in depth of tint 

 from the top to the bottom : this glafs is fet in a brafs frame, 

 which Aides in a dovetail between the azimuth plate and the 

 pillar ; and the elevation or depreflion of this is regulated by 

 a lever, the arm of which is readily brought to the hand in 

 any pofition ; this lever confifts of two feparate arms, which are 

 prefled together by fcrews, and each turn upon one pin inferted 

 into the pillar : by lightening the fcrews the fridion of the 

 arms againft each other may be fo increafed, that when the 

 longer arm is moved the fhortcr one moves with it, and raifes 

 or lets down the glafs-frame ; when this is raifed to the greatcft 



height. 



