44 PEACTICAL TREATISE ON 



scopic Journal, was delivered to the society. Tliis microscope 

 had the compound body mounted so as to slide in the groove of a 

 strong bell-metal arm, the contrivance of Mr. George Jackson, a 

 plan now adopted by Mr. Smith in all his large instruments; the 

 object-glasses were four in number, the highest being the 

 fourth of an inch, which, with the deepest eye-piece, was 

 capable of magnifying 800 diameters. During the last nine 

 years, Mr. Smith has made many and rapid advances in the 

 manufacture of microscopes, and, in conjunction with his 

 partner, Mr. Beck, has successfully endeavoured to reduce 

 the cost of his instruments by simplifying the form of stand, 

 by which they are brought more within the compass of those 

 whose means are limited. 



Amongst those in this country by whose agency the micro- 

 scope has been much improved, may be mentioned the names 

 of Mr. Varley and Mr. Pritchard, both of whom are well 

 known to the scientific world by their valuable publications. 

 To Mr. Varley, in 1831, we are indebted, first, for a micro- 

 scope with a lever stage movement, for following animalcules, 

 together with capillary cages for containing the same, fishing 

 tubes and other apparatus equally ingenious and useful, and 

 for his lathe for grinding and polishing lenses ; secondly, for 

 his vial microscope, for viewing the circulation in chara; 

 thirdly, for his graphic telescope and microscope ; fourthly, 

 for his valuable instructions and hints concerning the best 

 forms of eye-pieces for telescopes and microscopes ; and, 

 lastly, for his improved lever microscope, all of which in- 

 ventions have been fully described in the Transactions 

 of the Society of Arts. To Mr. Pritchard, we are in- 

 debted for three valuable works on the microscope, viz: — 

 The Microscopic Cabinet, The Microscopic Illustrations, and 

 The Micrographia, in which are admirably explained the con- 

 struction of the instruments made and improved upon by 

 Dr. Goring and himself, together with the history of the 

 doublet, jewel, reflecting, and achromatic microscopes, the 

 methods of testing and using the same, with the descriptions 

 of many interesting objects observed by them. These works, 

 which were the first of the kind published in England, have 



