VOL. XL.] PHILOSOPHICAL TRANSACTIONS. 25 1 



Procopius, in his Historia Arcana, says, the emperor Justinus, not being 

 able to write his name, had a thin smooth piece of board, through which were 



cut holes in form of the four letters^ W ^'HT' which, laid on the paper, 



served to direct the point of his pen; which being dipped in red ink, and put 

 in his hand, his hand was guided by another. Possibly this may likewise have 

 given the hint to the first of our card-makers, who paint their cards in the 

 same manner, by plates of pewter or copper, or only pasteboards, with slits in 

 them in form of the figures that are to be painted on the cards. 



An Occultation of Mercury by Venus, May 17, 1737} observed at the Royal 

 Observatory at Greenwich. By J. Bevis, M. D. N" 430, p. 394. 



At Q** 43"* 4' p.m. app. time. Mercury was only the 10th or 12th part of 

 Venus's diameter distant from her; afterwards the view was intercepted by 

 clouds. 



At 9*" 51™ 10' Venus shone out again very bright, and Mercury was quite 

 covered by her. Afterwards clouds again prevented any further view of the 

 phenomenon. 



Of a netv Azimuth Compass, for finding the Variation of the Compass or Mag- 

 netic Needle at Sea, with greater Ease and Exactness than by any ever yet 

 contrived for that Purpose. By Capt. Christopher Middleton, F. R. S. 

 N° 450, p. 395. 



To discover at sea the declination of the magnetic needle, or variation of 

 the compass, with some tolerable degree of certainty and exactness, is a thing 

 of great use and importance in the art of navigation. The instruments and 

 methods hitherto used for this purpose, are subject to several inconveniencies, 

 errors, and defects; to remedy which, this new azimuth compass was contrived, 

 which has by experience been found effectual. It would be needless to give a 

 description of the instrument; the cap therefore only shows the manner of 

 using it, which is as follows: 



1 . The instrument must be rectified, or fitted for observation, by turning it 

 about till the 4 cardinal points, that are hung on the centre pin, agree with 

 the 4 cardinal points on the chart, at the bottom of the box ; then will the 

 needle, that shows the magnetic meridianj stand at no degrees, and the east 

 and west points at go degrees, on the graduated circle within the box ; and in 

 this situation it must be kept, as near as may be, during the whole time of the 

 observation. 



2. Let the index of the quadrant be placed to that degree of the arch, on 



K K 2 



