270 M E M O I R S s/^ /Z^^ 
fide of the focket comes a fliort arm G, with a fcrew-hole to 
receive the long fere w II, whofe length may be about fix 6r 
feven inches 5 its lower end, by a fmall hole in its centre, refls 
on the end of a fmall fcrew, that comes thro' the fcrew-hole in 
the arm H, which is fixed on the back-fide of the column 5 the 
upper end of the fcrew is filed lefs than the body of the fcrew, 
and goes thro' the centre of the round plate without fliaking 5 
and to prevent its doing fo, either upwards or downwards, there 
is added a fpringing plate ;/, which*^ keeps the fhoulder of the 
fcrew clofe to the under fide of the plate K; over this plate 
there goes an index (?, and over that an handle L, upon the 
end of the fcrew, which comes thro' the centre of the plate, 
which is rivetted to the top of the column B B 5 the teeth of 
the fcrew mufl be of that lize, as to have juft 10 in an inch; 
the fore-fide of the column muft be divided into inches and 
tenths, beginning about the height of the focket H, where the 
lower end of the fcrew refts, and fo continuing to the top of 
the column 5 the limb of the round plate muft be divided into 
100 parts- in the Focus of the eye-glafs of the microfcope is 
fixed an hair, or very fine filver wire, in an horizontal pofi- 
tion : When you ufe this inftrument, take hold of the handle, 
and looking thro' the microfcope, turn the fcrew till you have 
brought the hair to touch, as it were, the furface of the mer- 
cury raj then obferve what divifions are cut on the column, by 
the upper or under edge of the focket which are tenths of an 
inch j obferve likewife to what parts the index pomts on the 
limb of the round plate, which are hundreds of a tenth, or 
thoufand parts of an inch 5 when you perceive the mercury 
varied, raife ordeprefs the microfcope, till the hair be brought 
to its furface, as before- then by fubftra61:ing the lefTer from 
the greater of the two obferved numbers, you will have the 
variation in inches and thoufand parts : This inftrument be- 
comes a micrometer on the fame principles 5 the thermometer 
is alfo capable of the like improvement. 
^he chief Ufe of Refpiration; by 'Br, V/ill. Mufgrave. Phil. 
. Tranf. N° 240. p. 178. 
DR. Thurfton afTerts, that the chief ufe of refpiration confifts 
in maintaining a due motion of the blood 5 but his argu- 
ments fecming to be infufficient. Dr. Mufgrave pitched on the 
followinrx experiment: He took a large, middle aged healthy 
dog, and having freed the Trachea from the adjacent parts, he 
cut it off juft beneath the "Tomura Adaraiy and turned the 
loofe 
