148 MICROSCOPIC ILLUSTRATIONS. 



for a pleasing view. When we want to examine these 

 objects merely for the purpose of amusement, it will be 

 advisable to use compound instruments, on account of 

 their large field of view, luxurious accommodations, and 

 arrangements : their powers must be made equivalent to 

 the single lenses I employed, namely, one inch, half an 

 inch, and a quarter of an inch focus, which require their 

 objectives to be about four, two, and one inch focus re- 

 spectively, (as the weakest compound body which can 

 be applied usually quadruples the power of the object- 

 glass.) For the reasons stated above, all the requisite 

 motions and adjustments must here also be given to the 

 optical part, and not to the stage. It will also be found 

 a very great convenience if the stage is so constructed as 

 to admit of being altogether removed, so that any large 

 body, such as a square vase on a large flat slider, con- 

 taining the objects, can be substituted in its place, in 

 order that there shall be no necessity to remove the 

 insects from their usual places of abode in the said 

 vessels, &c. as they are very apt to receive injury and 

 become restless by such removal. In order to effect this 

 very desirable arrangement successfully, it will be neces- 

 sary that the bar of the microscope, instead of working 

 upon the stand with a cradle joint, should possess a ca- 

 pability of turning round by moving in a ball and socket, 

 or some other similar contrivance, so that the space 

 occupied by the stage may fold down on one side, and 

 allow of the introduction of the jar, &c. into it on its ap- 

 propriate stand; when, all the necessary adjustments 



