( 7ooj ) 
the appearance he mentions. Howevir this may be* 
to prevent any difpute, and avoid the coming to 
Utri creditis, Omrites > I fhall offer a Teftimony, that 
every body will be fatisfy’d with, namely that of the 
learned and ingenious Mr. Machin, Profenor of Afiro^ 
mm'j in Grcjham CoUedge^ and one of our Secretaries, 
who having honour’d me with his Company at a re- 
petition of this Experiment, in order to be witnefs to 
the Event, was fully fatisfied upon repeated tryals, 
that there v/as no perceivable difference between the 
Magnitude of the Blood Globules in the Air, and in 
Vacuo. Upon this occafion the two firfl: Experiments 
were likewife repeated in his prefence, with the fame 
Succefs, as above related. 
Though what has been already faid is a fufficienc 
proof of the Opinion above- mention’d, yet however 
to prevent the Objedbions, which may arife for want 
of Experiments made in the fame manner with Mr. 
Boyle% as well as for the fatisfadion of the Curious, 
who may be defirous to know the true Specifick Gra- 
vities of Serum and Blood, I lhall proceed to demon- 
ff rate^ the fame thing by Hydroftatical Experiments. 
Exp. V. Novemh. 13. 17 13. Having fuffer’d a quan- 
tity of my own Blood to Hand about 24 Hours in 
the Porringer, and then drawing off the Serum carefully 
with a fmall Siphon into a convenient Glafs, 1 found 
by the Hydroftatical Balance it’s Specifick Gravity to 
be to that of Water, as 1029,8 to 1000^ 
Exp, Vf* Feh, a 1. 1716-7. I examin’d the Serum 
from the Blood of another Perfon in the fame manner 
and found it’s Specifick Gravity to be 1028,6. 
Exp.Vll. VIII. and IX. April 8th, 1717* I obtain’d 
three feveral quantities of Serum ftom the Blood of 
different Perfons. The firfl: of thefe wasj of a deep 
9 0^2 colour. 
