Meafuremeni of a 'Bafe on Hounflo^v-Heath. 46? 



the firil: of tliefe, two (Irong pieces of brafs, fixed to the cheeks, 

 and notched underneath, embrace the ends of a brafs cylin- 

 drical bar faftened to the bottom. At the laft, the cheeks of 

 the Aide reft on a roller. Whence it follows, that the copper and 

 Hide remain immov^eable with regard to each other at A ; but 

 ll from thenJe, towards either end, they have fall liberty to 

 •change place ; that is to fay, to expand by heat, or contrail by 

 cold, in any proportion their different natures may require. 

 The left-hand end of the Aide is (hut up by a ftrong perpen- 

 dicular piece of brafs, conne6led with the two fide rings which 

 fupport the object lens of the fixed microfcope, whofe center 

 correfponds accurately with its inward face. This piece being 

 firmly fcrew^ed to the checks of the Aide, and counter-arched 

 outwardly, forms a flrong butt for the fixed end of the ex- 

 panding rod (fuppofed here to be the fleel bar) to acl againil. 

 Within the right-hand end of the long Aide, reAs a Ihort one 

 -of about 14I inches in length, whofe cheeks are i 5 inch deep. 

 Its outward end, at C, reAs on the cylindrical furface of the laA: 

 brace of the long Aide, fitted purpofely to receive it ; while a 

 narrow longitudinal bar fixed in its inward end, at DE in the 

 fedlion, moves freely in the notch of a bridge F, framed for it 

 ^in the long Aide. The outward end of this Aiort Aide is Aiut 

 up in a fimilar manner with the oppofite end of the long one. 

 This end-piece is al'fo conneded with the two fide rings 

 which fupport the tube containing the object lens of the mi- 

 crometer microfcope, whofe center is perpendicularly over its 

 inward face, and being fortified outwardly by an edge bar, it 

 forms a butt for the expanding end of the rod that is in experi- 

 ment to puAi agaiiift. ^y attending to the plate it will be 

 perceived, that to this end of the boiler a brafs tube (R) is 

 fixed, which contains within it a brafs rbd, furrounded by a 



V p p 2 helical 



