(178) 
This Inftrument becomes a Micrometer on the fame 
Principles, tho' I was obliged to alter its Strudure from 
that ufed with the Telefcope, which was firft invented 
by Mr.Gafcoign, improved by Mr rw/f/y, aoddefcribed 
by Dr. Hock^ as appears by Nami. 25. and 29. of 
Mr. Oldenhurgs Philofofhical Tranfa^ions ; to w hich Dc- 
fcription, it 1 did not acknowledge my felf beholden, 
were to do great Injuftice to the Authors of that excel- 
lent Invention. 
The Thermometer is capable of the like Improve- 
ment, but then the Screw of the Micrometer muft be 
much longer, and the Microfcope will require a longer 
Tube, to the End the Body of the Obftrver be not too 
near the Thermometer, and by its warm Effluvia deceive 
his Judgment in the Air's Temperature. 
CanUrhury^ May 
1698. 
IV- ?m of a Letter from Dr. William Muf- 
grave, Fellow of the College of fhyftcianSy 
and R. to Dr. Sloane , concerning the 
Caufe of the Necejpty of Breathing. 
YOU know, bow difficult it has been thought^ 
to account for the principal Ufe of Refpiration : 
Nothing is more evident, than that breathing is, from 
the very Moment of our Birth, perpetually necellary ta 
Life; yet nothing more in the Dark, than the true 
Cauft and Reafon of that NecelTity. 
Dr. ThruftoH aflerts the chief Ufe of. Refpiration, ta 
coaf^ ia maintaining a due Motion of the Blood. 
