OBSERVING WITH AND MANAGING ENGISCOPE. 193 



though somewhat tedious, none but the veritable rmcra- 

 scopic crystals are obtained. Deliquescent salts, in damp 

 weather, can, however, hardly be brought to consolidate 

 in this way. 



I hope the description of the method of management 

 is now tolerably complete, as concerns transparent inani- 

 mate objects ; but the method of dealing with living ones 

 requires some illustration. 



4th. Way of Mounting for Transparent Living Objects* 

 These are not seen well by artificial light, as I have 

 already observed, their internal machinery being more 

 or less confused by it, whether its rays come diverging, 

 converging to a focus, or parallel. 



It will be rather difficult to get a power low enough, 

 with the present instrument, to obtain a general view of 

 a number of the larger aquatic larvae ; for I do not think 

 the present engiscope will carry an object- glass of longer 

 focus than two inches ; which, with the lowest inverting 

 eye-piece, will be fully twice too high (for, be it ob- 

 served, the lower the power is the more of an object it 

 will include in the field of view, and the higher the less); 

 but, with the erecting eye- piece thrust pretty far into 

 the body, a power will be obtained that will easily in- 

 clude a space of one and a half, two, or even three 

 inches ; therefore use the erecting glasses A, screwed 

 on to the bottom of the internal tube of the body, and 

 draw it in or out, until it just takes in the area of your 



o 



