290 An Account of some Experiments 



the author of the English formula is wrong in stating that it wil 

 give the value of the correction with perfect accuracy ; and the 

 Commissioners of Longitude ought not to have sanctioned such 

 an assertion. In the present state of astronomy, and when a 

 new impulse seems to be given to the science, every one must 

 hail with satisfaction any attempt to expedite and facilitate the 

 laborious calculations which too frequently arise in pi actice : and 

 no one is more sensible than I am of the ability and disposition 

 of the members of the Board to encourage such attempts. Let 

 us not however retrograde in the science, but endeavour to im- 

 prove on what has gone before: so that we mav eventually hope 

 to regain that proud pre-eminence from which we have been 

 driven by our more industrious neighbours. 



1 am, sir, your obedient servant, 



Philaster. 



XLIV. An Account of some Experiments on the Flexihllitij and 

 Strength of Stones. By Mr. Thomas Tredgold. 



To Mr. Tilloch. 



Sir, — In these experiments the piece under trial was supported 

 at each end upon iron supports ; the scale for the weights was sus- 

 pended from ihe middle between these supports ; and a silken 

 line, attached to the middle, moved a lever index ; which mul- 

 tiplied the depression so as to render a very small quantity vi- 

 sible. 



The scale and its apparatus weigh ten pounds ; and the 

 weights I use are cubical pieces of iron, cast for the purpose, of 

 10 lbs. each. Weights of this kind pack neatly together upon 

 the scale, and there is less risk of error in counting them than 

 common weights. 



The weight in the scale was increased bv 10 lbs. at a time, 

 laid on as softly as possible, and the index was always allowed 

 to become stationary before another addition was made to the 

 weight. The time which elapsed before the index became sta- 

 tionary was not observed, but it always increased sensibly to- 

 wards the end of the experiment. 1 had the advantage of my 

 brother's assistance in making the experiments where the flexure 

 was measured. 



Detail of Experiments. 

 1. A piece of white statuary marble, of a very regular texture, 

 free from veins, or other apparent defects, was tried at three 

 different lengths ; the short specimens were the fragments of the 

 long one. The piece was not perfectly uniform in breadth and 

 depth, but the dimensions at the places of fracture are given. 



Distance 



