Microscopical Essays, 



lenfes. When the three lenfes are ufed together, it is beft to turn 

 them into the cafe, and look through the hole, as this combined 

 magnifying power is fo great, that it requires to have a portion 

 of the light which falls on the lenfes excluded, in order to attain 

 diftin6t. vifion. Further, the eye is alfo by^ this means made to 

 coincide more eafily with the axis of the glafles. 



Description of a portable Microscope and Telescope, 

 Fig. i, 2, 3, 4, 5, 6, Plate VIII. 



The telefcope is one of thofe which are compofed of feveral 

 Aiding drawers or tubes, for the convenience of being put in the 

 pocket; the Hiding tubes are made of thin brafs, the outfide tube 

 of mahogany. 



The Hiding tubes are contrived to Hop when drawn out to a 

 proper length, fo that by applying one hand to the outfide tube, 

 and the other hand to the end of the fmalleft tube, the telefcope 

 may be at one pull drawn out it's whole length ; then any of the 

 tubes (that next the eye is molt generally ufed) may be pufhed in 

 gradually while you are looking through, till the object is ren- 

 dered diftinct to the fight. 



To make the tubes Aide properly, they all pafs through fhort 

 fprings or tubes ; thefe fprings may be unfcrewed from the ends 

 of the Aiding tubes by means of the milled edges which project 

 above the tubes, and the tubes taken from each other if required, 

 and the fpring fet clofer if it is too weak. 



