On the Effect of Aberration in prismatic Interference. 191 



ground. The portions of ice (with a single exception) were 

 formed at the edges of the stones, — indifferently at the tops, the 

 bottoms, or the sides, but the curvature was uniformly turned 

 inward from the mortar. There was a single instance of for- 

 mation on the mortar itself, in which case the threads of ice 

 were formed in an horizontal line, and I think (for of this I 

 made no memorandum) parallel to the layer of mortar. 



There was a considerable extent of old wall in the same 

 situation, but the ice was only found on a part, which had 

 been recently built. In looking back to the meteorological 

 journals kept at the Observatory, I find the following entries: 



1821. Feb. 17. 12 h 30' Thermometer out of doors 31° thick fog. 



10 30 — - — — 29 cloudy. 



18. 8 30 — — — 34 cloudy. 



12 30 — — — 38 cloudy. 



May not, therefore, the new mortar be supposed to have 

 supplied the moisture which was congealed by the radiation 

 from the sharp edges of the new stones ? and as water expands 

 in freezing, though ice contracts after it is frozen, may not the 

 curling form have been produced by the greater cold retained 

 in the stone from the frost of the preceding night? 

 I remain, dear Sir, yours truly, 



Oxford, Feb. 2, 1833. S. P. RlGAUD. 



XXIX. On the Effect of Aberration in prismatic Interference. 

 By William R. Hamilton, Esq. Andrews' Professor of As- 

 tronomy in the University of Dublin, and Royal Astronomer 

 of Ireland*. 



HPHE experiments and reasonings of Mr. Potter respecting 

 -*• the phamomena of prismatic interference, published in 

 the last Number of the London and Edinburgh Philosophical 

 Magazine (for February 1833), deserve attention; for, if cor- 

 rect, they would furnish a formidable and, perhaps, fatal ob- 

 jection against the undulatory theory of light. I have not re- 

 peated the experiments, but I have endeavoured to examine 

 the mathematical part of the question, and have obtained re- 

 sults which differ from the mathematical results of Mr. Pot- 

 ter, and which appear to show that the phenomena described 

 by him are consistent with the undulatory theory. It may, 

 therefore, be useful to state briefly some of my results, in a 

 form adapted for comparison with those of which they profess 

 to be corrections. In stating them, it cannot be supposed 

 that I intend any personal attack on Mr. Potter, for whose 

 talents and industry I feel a sincere respect. 



* Communicated by the Author. 



