68 The " Popular Microscope." 



adapted for binocular use, and as the cc Popular Microscope " 

 has the universal screw, it will carry any of the more expen- 

 sive and first-class objectives that might be desired. 



The microscope before us is supplied with a single combi- 

 nation focussing rather more than three inches from the 

 object, and taking in an object more than three-eighths of an 

 inch diameter. This is a very useful power, and the lowest 

 we have seen of achromatic make. Then there is a good 

 inch, and a good quarter, the latter working very fairly with 

 the binocular, which is seldom the case with low-priced glasses 

 of that focus. 



We tried this quarter on our own instrument, using an 

 achromatic condenser with stops. With our third eye-piece, 

 bringing the magnification to about 600 linear, we obtained a 

 distinct resolution of the Pleurosigma angulatum into dots. 

 Of course the defects of the glass were shown, as Messrs. 

 Smith and Beck state ; but we were surprised to find a low- 

 priced objective of only 75° aperture do so much. A similar 

 trial with the Podura scale was equally effective. There was 

 more colour than when a first-class quarter is employed, but 

 the definition was correct, showing even the spots of light on 

 the wedge-shaped markings. We notice that an achromatic con- 

 denser is supplied with the Popular Microscope, but it is not 

 of much use, for want of stops. Two stops would be quite 

 sufficient, and would only add a few shillings to the expense ; 

 one should exclude the central, and the other the marginal 

 rays. The plurality of stops in expensive condensers is cer- 

 tainly very valuable for special niceties; but the great ma- 

 jority of work can be done with two, one adapted to show such 

 lined objects as the angulatum, and the other fitted for the 

 general examination of objects in which penetration is needed, 

 and the marginal rays are better shut out. 



The public are now able to buy microscopes at a great 

 variety of prices and various proportionable degrees of merit. 

 They should be cautioned on the one hand not to expect im- 

 possibilities, or fancy that anybody will give them a hundred 

 guinea instrument for twenty pounds ; and on the other they 

 should be guarded against a tendency, prevalent in some 

 quarters, to undervalue instruments that are substantially 

 good, though not the best. Nine-tenths of the most important 

 discoveries have been made with objectives much worse than 

 those which respectable opticians now supply as avowedly 

 second-rate ; and it is only after long practice, and when a 

 large amount of information has been acquired, that the finest 

 glasses became more useful to students than those which, 

 being only a little below them in quality, can be had for half 

 the price. 



