102 THE POPULAR SCIENCE MONTHLY. 



but, to commence operations with, purchase the best 1-inch and ^inch 

 your means will permit. I much regret that the objectives made by 

 Gundlach, of Berlin, are not introduced. It would be a boon to those 

 who cannot afford to purchase the best glasses. I have seen them 

 tested at the Royal Microscopical Society with the most costly ob- 

 jectives, where their performance has elicited the highest praise. 

 When I state that an immersion -^^ costs in London but 3 10s., 

 the price of the low powers can be calculated. 



These ^V^^^ have wonderful definition, and can be used upon all 

 slides, having the ordinary thin glass cover, a great advantage. Such 

 a glass could be sold here for thirty dollars, and the 1-inch and ^-inch 

 for about ten dollars apiece. Except for special work, these objec- 

 tives answer every purpose. The sketch at Fig. 1 is a correct draw- 

 ing of the complete instrument, in position for use ; and at Fig. 2, the 

 same folded, showing its convenience and portability. The whole 

 weighs about a pound, and can be carried, with eye-piece and object- 

 glass ready for use, either in a bag or a light box 14 x 3^ X 3 inches. 



Those who possess very large instruments will find this model a 

 most useful addition for occasional use when traveling or demonstrat- 

 ing subjects away from home. 



This form of microscope is offered as convenient for beginners, 

 who, unable to purchase a complete instrument, still wish to make a 

 beginning and start upon a right principle. Although a complete 

 microscope can be purchased for about the same amount that the 

 optical portions of this will cost, it will be wanting in the chief es- 

 sentials of a good working instrument. Diminutive size, smallness of 

 field, poor light, shortness of tube, absence of Society's screw, and 

 other evils, will soon cause it to be cast aside, resulting in the loss 

 of the original outlay ; whereas the parts purchased under the above 

 directions are portions of a first-class instrument, obtained in advance, 

 which will never become obsolete. 



The immense field of inquiry within the grasp of the microsco- 

 pist is apt to disconcert and confuse the student. His course, how- 

 ever, should be well defined. First let him familiarize himself with 

 what has been done by others, and then confine his attention strictly 

 to those subjects which have reference to his profession or pursuit. If 

 he has no special occupation, I would advise him to select a particular 

 line of study, and let that be the thread on which to string his sub- 

 sidiary matter, mounting his own objects, and carefully registering his 

 observations. He will thus slowly but surely accumulate knowledge 

 that will benefit the cause of science. 



