VOL. XLIV.] PHILOSOPHICAL TRANSACTIONS. 263 



evaporated, the magnetical power took place. The cure for this inconvenience,' 

 is to moisten the surface of the glass: even a wet finger will do it immediately 

 and effectually. 



I need not suggest, that the same quantity of friction will not at all times 

 have the same effect on these glasses, any more than it will on the electrical 

 tubes ; but I have reason to believe that glass sometimes becomes in some degree 

 attractive without any friction at all ; and may possibly be excited by great con- 

 cussions in the air, such as thunder, or the discharge of great ordnance, &c. 

 and if so, may thereby disturb the compass. 



I must however observe, that the mariners' compass is much less dangerously 

 moved by wiping or exciting the glass than the other ; because the excited parts 

 of the glass attracts that part of the chart which lies nearest, just underneath, 

 without giving it so much verticity, as it does to the other sort of compass with 

 a bare needle. And further, that the deeper, or the farther distant the needle 

 hangs below the glass, the less disturbance it is likely to receive, by wiping, rub- 

 bing, or otherwise exciting the cover. 



I shall make no further reflections on these facts than to observe, first, that 

 all the minute, irregular, reciprocating variations, which have been observed in 

 the directions of dipping and horizontal needles, mentioned in some of the 

 Transactions, as N° 425, may probably have been caused by the glasses which 

 covered the instruments. And, secondly, that the flat pieces of glass, often 

 placed under the scales of an essay-balance, are likewise very capable of attract- 

 ing, and making even the lighter scale preponderate, where the whole matter 

 weighed is so very small. I have not tried this last, but I remember, that Mr. 

 Ellicot some years ago suspected, if he did not find it certain, that such pieces 

 of glass disturbed his balance, and had given him a vast deal of trouble, on a 

 supposition, that the beam itself was defective. 



Concerning some new Electrical Experiments lately made at Paris. By Mr. Tur- 

 berville Needham. N° 481, p. 247. 



These are the curious experiments of M. le Monnier. His electrifying glass 

 is an oblong spheroid ; the diameter fi-om pole to pole is 4 or 5 inches longer 

 than that at the equator, which is about 1 2 inches. Each of these poles is ter- 

 minated in a stem, or portion of a hollow cylinder, about 3 inches in length, and 

 1 in diameter, spirally embossed on the outside into a large male screw. This is what 

 they use here instead of our tubes, and with surprising effects, such as greatly 

 surpass what have yet been seen in England. The electrifying spheroid is turned 

 by means of a wheel about 4 feet in diameter, with the same motion, and exactly 

 in the same manner, as the spindle is turned round by the spinning-wheel : al- 



