Remarks on a Micrometer, &c. 433 
For Example.——An Object, or Part of 
an Object, whofe Diameter when viewed 
through the Magnifier N° 1. appears the 
exadt Length of one Square of the Hair 
Micrometer, is really no more than the 270th 
Part of an Inch in Length. 
And if, when viewed through the fame 
Glafs, it appears to fill up the whole Space 
of one of the faid Squares, its real Area is 
no more than the 72900th Part of a Square 
Inch, &c. 
In order to render this Infirument ftill 
more ufeful, Squares may be drawn on Paper 
(with very black Lines) correfpondent to 
thofe of the Micrometer magnified by the 
Eye Glafs, viz. -fo ths of an Inch Diameter ; 
by the Means whereof, (if placed under fo 
thin a Paper as they can plainly be feen 
through,) an Object may be drawn exactly 
of the Size it appears when magnified by 
any Glafs whatever.-Nine Squares fo 
drawn are fhewn Plate XVII. Jig. 6. 
In the fame Plate, fig. 4 fliews a Micro¬ 
meter whofe Divilions are the Fiftieths, and 
fig . 5, another whofe Divifions are the Tenths 
of an Inch : And this lafl may remain in 
the Body of the Microfcope, without being 
any Hindrance, whatever Glafs is ufed. 
J Twere well if the Workmen ground 
their Glaffes fo exactly to a Standard, that 
the fame Table might ferve for the Micro- 
m eter to every Set of them ; but as that is 
Vol. II, F f not 
