340 THE AMERICAN MONTHLY [Nov 



with similar numbers marked on the objectives ; the body- 

 remained clamped at the given mark until the objective 

 was changed, all the necessary focussing being performed 

 by means of the direct acting screw. The great advance 

 made in this model consists in the pivoting of the lower 

 end of the bar, a, on a ball and socket joint, h. As the 

 stage, d, is also fixed to this bar it is obvious that when 

 the instrument is inclined the stage is also inclined with 

 it. This feature is totally distinct from the " telescope 

 mount," and is one specially important in the evolution 

 of the microscope. — Queket Club. 



Examination of Water. 



By GEO. C. WHIPPLE, 



NEWTON CENTRE, MASS. 



The microscopical examination of water is becoming 

 every year a matter of greater interest, and the study of 

 the minute aquatic plants and animals is more and more 

 attracting the attention of scientists. These organisms 

 are interesting for several reasons and, besides recogniz- 

 ing their importance in the domain of pure science, we 

 are beginning to appreciate the great part that they play 

 in nature and their effect, direct and indirect, upon the 

 human being. Their presence in surface waters is often 

 the cause of much harm when the water is used for pur- 

 poses of domestic supply; scores of instances may be 

 mentioned where they have rendered the water entirely 

 unfit for use. On the other hand, their presence in ponds 

 and streams is of importance to the fish-culturist because 

 they form the fundamental source of the food supply of 

 fishes ; this is probably true both of salt and freshwater. 

 Because of the connection between the number of micro- 

 scopical organisms in a cubic centimeter of water and the 

 price of fish in our markets, the study of the 'plankton,' 

 i. e., the floating micro-organisms, is being emphasize a 



