PROCEEDINGS OF THE SOCIETY. 123 



possibly be produced, and becomes an absurdity. But supposing for a 

 moment we really had a conical wave-front, let us see how Mr. Gordon 

 employs it in the solution of problems. For this purpose the well-known 

 principle of Huyghens is invoked, the principle which shows how you 

 may arrive at the state of the light on lone surface, if you have a wave- 

 front travelling towards it, by regarding every point on the wave-front 

 as a new source, or centre, from which rays start forward in all directions, 

 and then examining what the resultant phase is, on points of the new 

 surface, of rays which have arrived there from every point of the known 

 wave-front. But how does Mr. Gordon apply these rules ? He does not 

 apply them at all, but simply transfers the result which they give, in the 

 case of a spherical wave-front, to that of the supposed conical wave-front. 

 That is, he alters the conditions entirely on which the result depends, but 

 nevertheless applies the result. 



While Mr. Gordon realises certain portions of the work of well-known 

 physicists — sometimes portions which have got neglected or overlooked, 

 and which it is a real benefit to have brought into prominence — he so 

 •entirely fails to grasp other and contingent matters explained by the 

 same authors, interspersing it with deductions that have never been 

 made, and improving upon it by laws of his own, which disregard 

 elementary optical principles, that the final result is an almost unexampled 

 confusion. 



Mr. Beck said he must protest against the kind of paper which had 

 just been read by Mr. Rheinberg, which might have been suitable in a 

 debating society in order to amuse the members, but in their own Society 

 their object was to arrive at scientific truth, and not to be entertained by 

 a dissertation upon what Mr. Gordon did, or did not do, or ought to have 

 done. It appeared to him that the question before them was drifting 

 into partisan lines, and if it were allowed to do that they would never 

 get any further towards truth in this direction. The paper of Mr. Gordon 

 was a very interesting resume of the work of Professor Airy and others, 

 and he thought the question of phase relation was an extremely interesting 

 one, as under all circumstances where they had two spurious discs they 

 probably had a dark line of some size between the two portions. As far 

 as he was aware, this observation was quite new. It was also extremely 

 interesting to be told of two wave-fronts being propogated in opposite 

 directions. 



Mr. Beck then referred to an optical apparatus exhibited in the room 

 to show the effect produced by the interposition of a grating. The object 

 was one of Grayson's rulings, the lines of which were almost invisible 

 until the grating was introduced, the effect of this always being to make 

 them more black and white — although he would not like to say that he 

 could see a finer band of lines with it than he could without it. 



Mr. Conrady said he quite agreed with Mr. Beck that personalities 

 should be kept out of scientific discussions, but he thought that such 

 considerations must not prevent them from inquiring into the validity 

 and accuracy of the statements contained in papers under discussion. 

 Having also had an opportunity of reading Mr. Gordon's paper in advance, 

 he had prepared the following remarks upon it. 



When a new theory is being proposed, one naturally looks first and 



