64 PHILOSOPHICAL TRANSACTIONS. [aNNO 1750. 



est part of the day, with a fresh breeze of wind at s.s.e. which terminated in an 

 evening extremely remarkable for appearances in the heavens of an uncommon 

 aurora borealia. At 15 minutes past 5, Mr. Sparshal noticed the foot of an 

 arch, which formed an angle of about 10° with the n.e. part of the horizon. 

 This arch shot out pointed streams like pyramids, of a fiery red colour, which 

 generally ascended within a few degrees of the zenith, then vanished, and were 

 immediately succeeded by others, from the n.e., where the principal magazine 

 seemed to be. They continually shifted towards the e. and s.w. with sudden 

 flashings and dartings ; but towards the west the appearances seldom altered. At 

 30 minutes past 5, a luminous stream, of a bright flame-colour, shot up on the 

 N. side of the fiery arch, which still kept somewhat of that form, though fre- 

 quently interrupted by shooting flashes from the n. e. At 40 minutes past 5, 

 there appeared suddenly in the n.e. an elliptical corona, of an amazing bright- 

 ness, elevated about 9° above the horizon, and having its longest diameter 

 parallel to it. There shot up perpendicularly from this streams resembling 

 columns of fliime intermixed with others of bright red. And so on, for various ' 

 other curious appearances. 



At the beginning of these lights the mercury stood at 29.9, but quickly fell 

 to 29.8. The wind at s.e. During part of the time there was an uncommon 

 motion in the magnetic needle. And this evening were seen several of those 

 meteors called falling stars ; particularly some which, on taking fire, left a long 

 train of sparks behind them. 



Description of a Mariner s Compass contrived by Gowin Knight, M.B., F.R.S. 



N° 495, p. 505. 



Almost all the compasses on board merchants' ships have had their needles 

 formed of 2 pieces of steel wire ; each bent in the middle, so as to make an ob- 

 tuse angle ; and their ends, being applied together, make an acute one ; so that 

 the whole represents the form of a lozenge ; in the centre of which, and of the 

 card, is placed the brass cap. Mr. M. procured 20 cards, with needles of this 

 kind fixed to them ; and after touching them with a pair of large bars, he tried 

 each of them, with the same cup and pin, by drawing them aside 90° from the 

 true point, and then seeing where they would rest. He found them all to vary 

 more or less, either to the east or west ; and some of them as far as 8°. Few of 

 them came to the same degree twice together ; and when they did, that was 

 never the true point. In short, they not only varied from the true direction, 

 but from each other, and from themselves. He then tried, by drawing them 

 gently aside, how far he could make them stand from the true point, without 

 returning ; and found they might frequently be made to do it at the distance of 



o 



