president's address. 37 



learn from excellent experimenters is practically monocliro- 

 matic. It is easily prepared and used, and although it yields 

 with lamp-light an orange light slightly tinged with greenish, 

 gives, for critical purposes, some beautiful results.* 



It will not, I feel assured, be inferred from the consideration 

 I give, and from time to time have given, to the higher or 

 highest powers of the microscope, that I am unconcerned for, 

 or have but little interest in, the object-glasses of low and 

 moderate power and the work to which they are applied. 



The fact is, that properly used, the dry apochromatic object- 

 glasses from an inch to a quarter of an inch in focal length 

 leave relatively little to be desired ; they are, so far as they go, 

 optical triumphs. Kot that they put a limit to my anticipa- 

 tion of what may be ; I look beyond them, in hope, and even, as 

 I think, in reasonable anticipation, to what is a still nearer 

 approximation to perfection. But that must be when physics 

 and chemistry have opened up new resoui^ces to the optician. 

 It is impossible to anticipate what may be discovered for us by 

 the steady and j^ersistent search of science into nature. That 

 new resources will present themselves to the electrician or the 

 photographer, we do not hesitate to believe. All recent history 

 makes the conclusion inevitable. I know of no reason why, in 

 like manner, some new possibility should not open itself to 

 practical optics. I see as much possibility of optical advance 

 in the futui^e as in the past. 



Meantime, however, the workers with low aiid moderate 

 powers of the finest construction (and they are ilow produced at 

 such moderate prices as to be fairly within the reach of most) 

 may well congratulate themselves on their possessions, and 

 work with a zest which their instruments certainly justify. 



Not only are the lenses good, but the optical appliances for 

 employment with them are equally admirable. 



We have passed the period when it was believed that all low 

 power and moderate lenses might be used without condensers. 

 Every compound lens is caused to do its best work with an 

 achromatic condenser adapted to its N.A. and its focal length, 

 and happily to-day these are accessible to all workers. 



* The solution is prepared as follows, viz. : — Sulphate of copper, 2ozs. 

 lidrs. ; bichromate of potash, Idr. 2scrup. ; sulphuric acid, 12min. ; water, 

 65OZS. 



