OF MICROSCOPIC OBJECTS. 19 



continual pressure. The power of this may be regulated by 

 the thickness and length of the whalebone. This simple con- 

 trivance is very useful. 



Common watch-glasses should always be kept at hand. They 

 are certainly the cheapest, and their transparency makes them 

 very convenient reservoirs in which objects may be steeped in any 

 liquid ; as it saves much trouble to examine cursorily under the 

 microscope, when the air-bubbles are expelled from insects, etc., 

 etc. They are readily cleaned, and serve very well as covers, 

 when turned upside down, to protect any objects from the dust. 

 For this latter purpose Dr. Carpenter recommends the use of a 

 number of bell-glasses, especially when one object must be left for 

 a time (which often happens) in order that another may be pro- 

 ceeded with. Wine glasses, when the " legs" are broken, may thus 

 be rendered very useful. 



As heat is necessary in mounting many objects, a lamp will be 

 required. Where gas is used, the small lamp known as " Bun- 

 sen's" is the most convenient and inexpensive. It gives great 

 heat, is free from smoke, and is readily affixed to the common 

 gas-burner by a few feet of india-rubber tubing. The light from 

 these lamps is small, but this is little or no drawback to their use. 

 Where gas is not available, the common spirit-lamps may be used, 

 which are very clean and answer every purpose. 



In applying the required heat to the slides, covers, &c., it is 

 necessary in many cases to ensure uniformity, otherwise there is 

 danger of the glass being broken. For this purpose a brass plate 

 at least three inches wide, somewhat longer, and one-eighth of 

 an inch thick, must be procured. It should then be affixed to a 

 stand, so that it may be readily moved higher or lower, in order 

 that the distance from the lamp may be changed at will, and 

 thus the degree of heat more easily regulated. This has also the 

 advantage of enabling the operator to allow his slides, &c., to 

 cool more gradually, which, in some cases, is absolutely neces- 

 sary, as in fusing some of the salts, &c. 



In order to get rid of air-bubbles, which are frequently dis- 

 agreeable enemies to the mounter of objects, an air-pump is often 

 very useful. This is made by covering a circular plate of metal 

 with a bell-glass, both of which are ground so finely at the edges 



