ON INSTRUMENTS AND THEIR USE. 29 



accomplish the work, also, the better. The use of 

 the higher powers, and the more delicate accessory 

 apparatus of the microscope follows when the pre- 

 parations are made, and examination and observa- 

 tion commence. As a matter of course, when 

 investigations have to be made during the progress 

 of the work, powers sufficiently high must be used, 

 but let it always be remembered that there is an 

 axiom, " all the best microscopical work has been 

 done with low powers " which, in reference to the 

 aims of this treatise, means all the best and most 

 perfect permanent preparations have been made 

 with low powers, and are afterwards to be studied 

 and examined under the higher powers and con- 

 ditions of light, &c., necessary to their elucidation 

 and use as valuable aids to scientific instruc- 

 tion. For many purposes such as the dissection 

 of the larger insects, or the teasing out of the 

 coarser tissues, a good " simple " microscope will 

 be found extremely useful; but, as a rule, it is 

 better to do almost everything under the compound 

 microscope, and to patiently acquire the necessary 

 skill which enables one to use both ordinary and 

 dissecting needles, small brushes, bristles, tubes, 

 &c., in the field of the microscope whilst using it ; 

 above all things it is important that, if possible, a 

 binocular microscope should be used when many 

 hours are spent in microscopical work, for not only 

 is it natural, and therefore better, to use both eyes, 

 but fatigue to the eyes is thus avoided, whilst it is 

 certain, in respect of those who work with one eye 

 only (unless the eyes are used alternately and often 

 changed) that one eye becomes educated at the 

 expense of the other, and to such an extent, that 



