( 8 49 ) 
muth of the greater Star is taken) by a Micrometer (confining 
of divers fine Threads parallel and tranfverfe) may (at the fame 
time) be obferved the Diftance of the two Stars, each fromo- 
ther, in that Pofition (both being at once wirhin the reach- of 
the Micrometer :) which diftance (the Inftrument remaining 
unmoved) if it be tound (at different times of the Year) 
not to be the fame-; this will prove, that there is a different Pa- 
rallax of thefe two v Stars. 
This latter part of the Obfervation (of their different di- 
fiances at different times)! fuggeft, as more eafily practicable 
though not fo nice as the former. For i: may be done, I think* 
without any further A^aratm there than a good Telefcope, 
of ordinary form* furniihed with a Micrcmeter, (this being 
carefully kept unvaried during the Interval of thefe Obferva- 
tigns.) And if this part only of the Obfervation (without the 
other) bepurfued ; it matters not though the two Obfervati- 
ons (near the two Solftices) be, one at the.Eaftern, the other 
at the Weftern Azimuth (whereby both may be taken in the 
Night-time J for the diftance muft (at both Azimuths) be the 
fame, if after obferving the Azimuth of the greater Star it be 
neceffarv to move the Micrometer for meafuring its diftance 
from Alcor that may be done another Night (and it is not 
neceffary to be done at one Obfervation) for that diftance 
cannot be ditcernably varied in a Night or two. 
I fhall give you no farther trouble at prefent, but fubfcribe 
my felf, Sir a Yours, Sec. 
IX. An Account of a BOOK. 
Synopfis Mtthodica Animzlimt QHddrupednm & 
Str^eniini Generis Anth. Joanne Raio 5 S.R.S. 
TK E Excellent Author of this Synods of Quadrupeds and 
Serpents, continues to oblige the- World with frefh and 
frequent Specimens, not only of his great Penetration in difc 
covering, but of his particular Sagacitv in ranging and digeft- 
ing the vaft Body of Nature in molt proper ClalTes and Orders • 
whereby the Memory is extreamlv affifted, and the Beauty of 
S f the 
