ssa 



Second move- 



person 



J'.ach 

 actsindepent- 

 antljr of the 

 rest. 



BURNING GfLASS OF ARCHIMEDES. 



tance from the axis of the telescope as the edge of t&e 

 frame is. 



Accordingly this right line being traced on the face of th© 

 index, for executing the first motion it js sufficient to tura 

 the telescope on its axis, till the shadow of the frame co- 

 incides with the right line on the index; v/hicb may be done 

 with considerable precision. 



For thesecondmovement, it is clear, that, when the mir- 

 ror is so placed as to have its reflected rays parallel to the 

 axis of the telescope, if in the axis of the mirror, and close 

 to the edges of the frame, a Kttl« Hne of the silTering be re- 

 moved, the want of silvering will pradtice a shadovr, that 

 will fall on the middle of the right line of the index. Thi» 

 middle point being previously marked on the index, to ex- 

 ecute the second movement it suffiees to turn the mirror on 

 its own axis, till the shadow of the unsilvered stroke falls 

 on this point; which may be done with the same precision 

 as the former movement. 



Thus we see, that every person employed, however great 

 the number, may direct the image he produces to the point 

 assigned for the focus, without troubling himself about 

 what is done by the others, and without being disturbed by 

 their operations. It may be observed too, that the motion 

 of the sun in its diurnal axis is not so rapid, but that one 

 person might attend to ten mirrors near each other, and 

 keep them in the right position, which would greatly dimi- 

 nish the trouble and expense of the process. 



We are of opinion therefore, that Mr. Peyrard has car- 

 ried the construction of burning mirrors composed of se- 

 veral plane mirrors to a degree of perfection, that it had no4; 

 before acquired, and appears to us to merit the approbation 

 of the class. 



Done at the Palace of the Arts, 3rd of August, 1807. 

 CHARLES, 

 ROCHON, 

 MONGE, Reporters. 



The class approves this report, and adopts its conclusions. 

 DELAMBRE, Perpetual Secretary.. 

 Paris, 4fh of August, 1807. 



XI. Analysis 



