Mr., iiersciiel's Account 
taveniir pfufieurs fois fur certe etoile ou Comete car' ah foils- 
menu if a; Mil l’bbferver pliilieurs jours de: flute pour; s’ap- 
**■ pergevoir qu’elle a volt un mouvementd 9 
I need! not fay that I merely point this out" as a temporary' 
advantage in the method I have taken for as foon as we can. 
have regular,, conftanty and 4 long, continued' observations by 
fixed 1 inllrumen ts„ the excellence of them is. too' well Known to> 
fiy any thing upon that fubjedi r for which reafbn I failed* not 
tSgive-immediate notice of this moving' fiat, and" was happy to> 
fu r render it to the care of the Altronomer Royal and others, as 
foon. as I found' they had begun their obfervations upon it. 
iDfcription of a micrometer for tailing the- angle of p ft ion*. 
FIG. I. Reprefents the micrometer inclo/ed in a turned cafe 
of wood, as it is put together, ready to be uled with the tele- 
foope. A is a little box which holds the eye-glafs. B is the 
piece which covers the iniide work, and the box A is ferewed 
into it.. C'is the body of the- micrometer, containing the brafs 
work,, foewing the index plate a projecting at. one. fide, where 
the cafe is- cut away to.. receive it. D is a piece,, having a ferew 
b at the bottom,, by means of which tire, micrometer is fattened 
to the telefcope. To the piece G is given a circular motion, in 
the manner the horizontal morion, is generally given to Gre- 
gorian reflectors,, by the. lower part, going through the piece D, 
where it is held by the ferew £, which keeps the two pieces 
C and D together, but leaves them at liberty to turn upon, 
each other.. 
Fig. II. Is a fedlion of the cafe containing .the brafs work-,, 
where may be obferved the piece B hollowed out ta receive the- 
3 box. 
