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his own admiration of the little instrument which had been brought under 

 their notice. The silvered surface as applied to microscope mirrors he thought 

 was a valuable introduction. 



Mr. Ingpen said he could vouch for the great amount of light reflected by 

 mirrors silvered in this manner, and to the advantage of having only one re- 

 flecting surface, but he should be glad to know if the silver did not soon become 

 tarnished, as this had been found to be the case with specula for telescopes 

 which had been silvered in this way. There was a great difi'erence in the films 

 deposited ; sometimes they were tolerably hard, but often they were very soft, 

 and the silver was then very easily rubbed ofi". Cos and Johnson's films were 

 generally soft ones. He had himself deposited many films by the sugar of milk 

 process, but found that in most cases they were easily tarnished and rubbed off". 

 His object in asking the question was the hope that some method of hardening 

 the films might have been discovered. 



Dr. Matthews said that he could not at present say much upon the point. He 

 had not yet attempted to clean the silver surface, although he found that there 

 was a finger mark upon it. 



Mr. Locke, having had some experience as to silvered glass reflectors which 

 had been done for him by Mr. Swift, could say that he had found them tarnish 

 very rapidly, and the films were so soft that any attempt at re-polishing rubbed 

 them away. He found this such an objection to their use that if he required 

 any more he should have them made of silver plate. 



Mr, Ingpen thought that silver plate would be found to answer the purpose 

 very well. He was quite aware of the objections to glass silvering, and had 

 asked the question now hoping to hear that some means might have been found 

 of preserving the surface. 



Mr. T. C. White could bear testimony as the value of this mode of silvering for 

 refiecting purposes. Some time ago he used a plane mirror silvered in this way 

 for drawing objects by inclining it at an angle of 45° with the horizontal body 

 of the microscope, and projecting the magnified image on to the drawing paper, 

 the reflecting surface was perfect, but he felt very much grieved to flnd that it so 

 soon got tarnished. He quite agreed with Mr. Ingpen that if only some method 

 of preserving the silver could be devised it would be invaluable for such 

 appliances. 



Mr. Ingpen said that the question was engaging the attention of several 

 persons at the present time, and was one of some importance now that so 

 many telescopes were being made with specula silvered in that way. When 

 the film was first deposited it of course had to be polished, and this was done 

 with a very fine leather and the finest rouge. Perhaps Dr. Matthews might be 

 able to remove the finger mark from his mirror by this means j some films being 

 much harder than others would bear more rubbing. Of course any mirror could 

 be re-silvered at any time at a small expense. 



Mr. Matthews said he had omitted to mention that he thought at first the 

 mirror had been made too small for the purpose, but he found it in reality to be 

 quite twice too large; it would be much better if it were made smaller. Prac- 

 tically one not wider that |in. in diameter would do quite well. 



Mr. Ingpen thought there could be no doubt as to the superionty of silver 

 surface over any other for reflecting purposes ; he had some small specula 

 belonging to Gregorian telescopes which were well polished and clean, but they 

 bore no comparison with the silver for the amount of light which they reflected. 



Mr. Ackland suggested that if Dr. Matthews would use as a reflector a double 



