Microscopical Essays. 



21 



fare, laid a fide. In 1770, Dr. Hill * publifhed a treatife, in 

 which he endeaf ours to explain the conflruction of timber by 

 the microfcope, and mew the number, the nature, and office of 

 it's federal parts, their various arrangements and proportions in 

 the different kinds ;• and point out a way of judging, from the 

 ftruclure of trees, the ufes they will befl ferve in the affairs of 

 life. So important a fubjecWoon revived the ardor for micro- 

 fcopic purfuits, which feems to have been increafmg ever fmce. 

 About the fame time, my father contrived an inflrument for cut- 

 ting the tranfverfe feci ions of wood, in order that the texture 

 thereof might be rendered more vifible in the -microfcope, and 

 confequently be better underftood ; this inflrument was afterwards 

 improved by Mr. Gumming. Another inflrument for the fame 

 purpofe, more certain in it's effects, and more eafily managed, is 

 reprefented in fig. 1, plate 9 ; it will be defcribed in one of 

 the following chapters. Dr. Hooke and Mr. Cuftance now en- 

 deavoured to bring back the microfcope nearer to the old ffand- 

 ard, to increafe the field by the multiplication of the eye glafles, 

 and to augment the light on the object, by condenfmg lenfes ; 

 and' in this they happily fucceeded :; Mr. Cuftance was unrivalled 

 in his dexterity in preparing, and accuracy in cutting thin tranf- 

 verfe feclions of wood,. 



In lyy i, my father publifhed a fourth edition of his Micro- 

 graphia, in which. he defcribed the principal inventions then in 

 ufe ; particularly a contrivance of his own, for applying the folar 

 microfcope to the camera obfcura, and illuminating it at night by 



a larap 3 . 



•* Dr. Hill on the Conftruaion of Timber, 



