1892.] THE MICROSCOPE. 147 



chase, always reserve the right to have them examined by an 

 expert. Have a distrust especially of all "nameless" objectives. 

 It is safe to assume that if the maker cannot attach his name he is 

 doubtful of their superiority. Any maker of responsibility will 

 say without hesitation that he can produce objectives at less than 

 one-half their present cost, if he had the assurance that they would 

 be accepted as first put together, as the costof merely making and 

 mounting lenses is considerably less than the cost of making 

 proper corrections. In this case, however, they would be of 

 varying and inferior quality. 



It is sometimes found that dealers offer the same objectives of 

 different quality at different prices. Too great care cannot be ob- 

 served in such cases, as the very fact of the admission of a differ- 

 ence in quality indicates that they are made by an unreliable 

 maker. This mode of offering objectives was in vogue many 

 years ago, when the principles of optics and facilities for making 

 were limited, and when a higher price was asked for those which 

 might be termed a happy combination. There is no excuse, 

 however, at the present day, for anything of this kind, because 

 every conscientious optician has his standard for every objective, 

 which is his guide. 



In purchasing a microscope, a beginner may be easily misled 

 by the enticing appearance of an object, which may be due not 

 so much to the instrument as to the object itself, and if the optical 

 parts are inferior it will require but a short experience to become 

 convinced of it — usually as soon as a comparison can be made 

 with reliable work. The investment in one of these objectives is 

 not only a source of disappointment, but usually proves to be a 

 pecuniary loss, as it is usually followed by a fresh outlay in 

 responsible work. It is of ordinary occurrence that such objec- 

 tives as have just been spoken of are sent to the writer's firm with 

 the request to examine them and rectify the faults ; but an exam- 

 ination almost invariably proves that the cost of doing this is 

 considerably greater than purchasing a new objective of the same 

 power, and it would not even then be equal to the latter. 



How to Collect Desmids. 



ByWM. N. HASTINGS, 



ROCHESTER, N. H. 



Desmids are microscopic unicellular fresh-water plants, and be- 

 long to the order Algce. Under favorable circumstances the 

 largest of them may be seen by the naked eye as minute green 

 specks in the water. The smallest of them require a good com- 

 pound microscope for identification, being of no greater diameter 



