106 SELECTION AND USE 



Tlte Stand. This should be firm and substantial, with, the 

 centre of gravity very low. Nothing detracts so much from the 

 performance of an objective as tremor and vibration, an da largo 

 majority of the microscopes in market are very shaky, from the 

 fact that they a-e made tall and showy in order to command a 

 higher price. It is well, therefore, to bear in mind that size is 

 no criterion of the value of a microscope. Instrument makers 

 very properly give the size of their instruments, and it generally 

 happens that the largest instruments by the same maker bear 

 the highest prices. Other things being equal, however, small, 

 compact instruments are altogether to be preferred. Some 

 years ago the rage was for large, showy microscopes, which 

 made a fine appearance in the office of the physician, and the 

 study of the naturalist. It was found, however, that in this 

 case efficiency was sacrificed to show, and all our best makers 

 are now catting down the sizes of their instruments, and making 

 them steady, substantial, durable and easily operated. 



There is, of course, a limit to the extent to which stands may 

 be reduced in size without sacrificing their efficiency, and some 

 makers seem to forget this. There are stands iu market that 

 are too small every way for anything but special classes of 

 work. The bodies are too small to secure efficiency in the eye- 

 pieces and objectives; the stage is too small to allow of the use 

 of slides of proper size, and there is no room beneath the stage 

 for the attachment of proper illuminating apparatus. All this 

 is as inconvenient as the three-feet-high microscopes of the end 

 of the last century. 



The weight of the stand is a subject concerning which many 

 seem to differ in opinion. One writer goes so far as to say that 

 no stand weighing less than fifteen pounds can be steady enough 

 for the performance of good work. It will be found, however, 

 that a judicious distribution of the material, and a proper con- 

 struction of the different parts, will more effectually resist the 

 usual sources of unsteadiness than any increase of absolute 

 weight. Of course, if it is merely desired to make the micro- 

 scope steady, in the sense that an inkstand is steady that is, 

 not liable to be tipped over weight is everything. But the 

 stands that are most difficult to tip over are not those that 

 resist vibrations most perfectly. For the latter a tripod with a 



