232 Laws of Metallic Reflexion, and Mode of 



be susceptible.* Indeed I have found that, in this instance, 

 the geometrical laws of the phenomena are by no means obvious 

 interpretations of the equations resulting from the analytical 

 solution of the problem ; and in endeavouring to verify such 

 supposed laws I have often been led to algebraical calculations 

 of so complicated a nature that it has been impracticable to 

 bring them to any conclusion, and I have been obliged, from 

 mere weariness, to abandon them altogether. On returning, 

 however, to the investigation, after perhaps a long interval of 

 time, I have usually perceived some mode of eluding the calcu- 

 lations, or of directly deducing the geometrical law ; and, when 

 the theory comes to be published in its final form, no trace of 

 these difficulties will probably appear. 



From the causes above mentioned, combined with frequent 

 absence from Dublin, the researches which I had entered upon, 

 respecting the action of metals upon light, have been hitherto 

 interrupted ; and as it may still be some time before they are 

 resumed, I venture, in the meanwhile, to submit to the Aca- 

 demy the results already spoken of, which were obtained on the 

 first trial of the instrument, and which afford the best data 

 that can yet be had for comparison with theory. 



The results, it must be confessed, are those of very rough 

 experiments, made one evening (about the month of July, 1837) 

 in company with Mr. Grrubb, before I had received the instru- 

 ment from his hands, and merely with the view of showing him, 

 when it was finished, the kind of phenomena that I proposed to 

 observe with it, and the mode of observing them. But the in- 

 strument was so far superior (in workmanship at least) to any 

 apparatus previously employed for this sort of experiments, 

 that it was impossible, without great negligence in using it, not 

 to obtain measures of considerable accuracy. I did not, how- 

 ever, at the time, set much value on these measures, because I 

 expected shortly to possess a series of observations made with 

 every possible precaution ; but having chanced to preserve the 

 paper on which they were noted down, I was tempted, a few 



* Proceedings, VOL- n. p. 174 (supra, p. 218). 



