Mr. G. G. Stokes on the Aberration of Light. 15 



2 affcms sugar . . . . C 24< H 22 O 22 



1 ... water .... H Q 



I ... gummy substance C 24 H 21 21 

 This substance is formed then from 2 atoms of sugar by 

 the abstraction of 1 atom of water. 



As a solution of the gummy substance gave a compound 

 with lead, we endeavoured to obtain by its aid its atomic 

 weight. 0*260 of the precipitate gave of lead and oxide of 

 lead quantities equal to 0*316 oxide of lead, which, when al- 

 lowance is made for ashes, is equal to 55*8 per cent, of oxide 

 of lead. We had not enough of the salt to enable us to make 

 the combustion, but have calculated the formula from the 

 quantity of lead. 



From 55*8 per cent, oxide of lead the atomic weight found is 

 4400-0. The calculated one is 4198*4. 



We had imagined that this curious change in sugar might 

 have been the effect of organization, but our friend Mr. John 

 Goodsir was kind enough to examine the substance, and in- 

 formed us that he could discover no trace of organization. 



V. Remarks on Professor Challis's Theoretical Explanation 

 of the Aberration of Light. By G. G. Stokes, M.A., Fel- 

 low of Pembroke College, Cambridge*. 



r|^HERE are a few points connected with Prof. Challis's 

 JL paper on the Aberration of Light, published in the num- 

 ber of this Magazine for November 1845, respecting which I 

 wish to offer a few remarks. 



In the first place I perfectly agree with Prof. Chailis, that 

 the explanation of aberration is really independent of the 

 manner in which light may pass through the eye; but I can- 

 not agree with him that it is necessary to suppose that we see 

 a star in its true place, and that it is the wire of the telescope 

 with which it is observed that is affected by aberration. The 

 following mode of viewing the subject, due to Boscovich, will 

 perhaps put the matter in a clearer point of view. 



If we wish to determine the real or apparent direction of 

 an object, we may, theoretically speaking, adopt the following 

 plan: — Let two small circular holes be so adjusted that the 



* Communicated by the Author. 



