VOL. XLVIII.] PHILOSOPHICAL TRANSACTIONS. AOQ 



gh 2i"» 3' The small Star eclipseil by the moon. 



28 48. . |3 eclipsed by the moon. 

 g 48 24. . |3 emerged from the moon. 



Eclipse of the sun, Oct. 25. 



20 30 10. .The eclipse had been some time begun; but, for clouds, could 



not be seen till now ; when the distance between the cusps, 

 measured with the new micrometer, applied to a 2 feet reflector, 

 was 12' 264-". 



21 15 23. . The distance between the cusps 29' 49''. 



18 6. . The distance between the visible limbs of the sun and moon 1 1' 32". 



22 18 56. . The distance between the cusps 24' J 2-J-''- 



The day before, about 10 in the morning, the sun's horizontal diameter was 

 32' 17". 



These measures were all taken when the sun continued visible but for a few 

 seconds, through the interstices of flying clouds; and yet from the nature of this 

 micrometer, they may be very safely relied on : though it would have been im- 

 possible to have catched any one of them vvith the common micrometer. 



The principle on which this most excellent instrument is constructed, was laid 

 before this Society last May : and it is to be hoped that Mr. Dollond will evince 

 the certainty of its measurements, from the least to the greatest angle it is capable 

 of comprehending; and that, under every consideration of reflexion as well as 

 refraction by spherical surfaces; so as to leave no room for such objections or 

 cavils, as otherwise may probably be brought against it. For our own parts, we 

 are fully satisfied of the justness of it, from a great variety of trials and compa- 

 risons. That which we have hitherto used, is the first that has been made of 

 the kind: and might perhaps have been better constructed in some respects, 

 though in nothing material. 



Applied to a reflector of only 2 feet, the scale is as large as the common mi- 

 crometer can have in a 40-foot refractor; and all is done without the help of 

 screws or wires; so that there is no need of illuminating. In virtue of such a 

 scale it is, that even fractions of seconds may be depended on : as we have found, 

 by often repeated trials on the diameters of the planets. These, as well as small 

 distances of stars, may be measured in all directions, with equal and almost 

 incredible facility, without a polar axis; as well out of doors, in a rough wind, 

 as within. 



XLVI. Concerning a Ciusttr- Polype,* found in the Sea near the Coast of 

 Greenland. By Mr. John Ellis, p. 305. 



This marine production, sent him by Mr. Collinson, appears to be an animal, 



* Vorticella encrinus. Linn. Peiinatula encrinus. Linn. Gmel. 

 VOL. X. 3 G 



