VOL. XXXVI.] I'HILOSOPHICAL TRANSACTIONS. 351 



GG, from being thrust out of the perpendicular by the pushing pipe fe, whose 

 lower point being put into a little hole at h, the upper wire or point, when put 

 into another little hole under the beam at d, is by means of the worm-spring 

 EF pressing against the plug e to drive forwards the said wire hD, made to push 

 the said beam upwards with the force of the spring, xss is a stand, to which 

 is fixed the pillar xc that sustains the balance; and it has also a slit ss to 

 receive a shank of the moveable plate gg, to be fixed in any part of the slit by 

 a screw underneath. 



Exper, — Hang on sb, as in the figure. Then let ef be so applied "to the 

 hole H, that its upper wire hok may go through a little loop at d, so as not to 

 thrust the beam upwards, but be in the same position as if it did, that by 

 hanging on the weight w, the brachium bc with Bb and fe may be counter- 

 poised; and tiien the action against d and h may be estimated without the 

 weight of the pushing pipe. 



Then drawing down the end of the wire k, thrust it into the little hole under 

 D, and B will be so pulled downwards as to require the additional weight of 

 4 ounces to be hung on at a to restore the equilibrium, when bh is 4 inches, 

 BD 3 inches, and the whole force of the spring equal to 10 ounces. 



It need not here be said, that for explaining the second case, sh is to be 

 suspended at d, with the plate gg fixed, to stop it at the place m, to keep it 

 from being pushed towards x, and that the upper end of GFEok must push 

 into a hole made under b ; in which case the weight p must be hanged at b, to 

 restore the equilibrium. 



P. S. To show experimentally that the force which the spring exerts in this 

 oblique trusion, is equal to lO ounces: take the beam ab, which weighs 4 

 ounces, from its pedestal ex, and having suspended at each end, a and b 

 3 ounces, support it under its centre of gravity by the pushing pipe ef, set 

 upright under it ; and it will be found that the beam with the two weights will 

 thrust in the wire kh as far as h, the place which the oblique trusion drives 

 it to. 



Uncommon Appearances observed in an Aurora Borealis. By the Rev. Mr. 

 Derham, Canon of Windsor, and F. R. S. N°4]0, p. 137. 



About 8 in the evening of Oct. 13, 17'28, at Windsor, was observed a con- 

 siderable streaming in the north, with such bright lances and columns as usual. 

 But at Redbridge none such appeared, only in the north, Mr. D. observed a 

 great thick, black bank of vapours ; the top reaching about 20° above the 

 horizon, without any convexity or curvature, as is usual in most of the stream- 



