gSO NEW PENDULUM. 



all of brafs. The parts which are of fteel are the middle wire, 

 including 0,6 the length of the fufpenfion fpring, is 39,3, firft 

 Expanfionsof P^i*" of wires 32,5, and the fecond pair 33,2. From experi- 

 briis and ftecU ments which I tried in the year 1794, I found my brafs to ex- 

 pand with 60* of heat 0,000640 on an inch, and my fteel 

 0,0003966. Smeaton obtained under tlie fame circumftances 

 0,0006444 for brafs, and 0,0003833 for fteel. Roy found 

 brafs to expand 0,0006316 and fteel 0,0003816. 



The above lengths computed from ray expanfions will I think 

 be found very corre6l; if they are tried by Smealon's, the pen- 

 dulum will feem to err in excefs, or gain with heat, about 0'',9 

 a day with 60® of Fahrenheit; if Roy\s be ufed, it will err 

 jilfo in excefs, under the fame circumftances fomething more 

 than one fecond. The above ftatement ftiews with what care 

 experiments of this kind ought to be condu(5^ed. All the di- 

 menfions are given in inches and decimals. 



If my pyroraetrical experiments turn out fuccefsful, they 

 v|nay likely be the fubjed of another communication; and I 

 , will referve till then my reafons for giving the preference to 

 my own expanfions in the conftnidion of the inftrument here 

 defcribed ; for this letter, being twice as long as I firft intended, 

 iliall now be concluded by, 

 Dear Sir, 



Your obliged and obedient Servant, 

 EDWARD TROUGHTON, 

 November 3, 1804. 



II. 



Jietter from W . Jess.op, Fftj. on (in Improvement in the Procefs 

 of hlajiing Rocks zvit/i Gun-powder. 



To Mr. NICHOLSON. 

 SIR. 



If I am communicating to you what you already know, you 

 will accept as an apology for it that it is not generally knowii, 

 and will be interefting to all who are concerned in mining or 

 blafting rocks with gunpowder. 

 Vfual procefs of The uAial procefs, after drilling a hole and charging it with 

 boring and powder, is to introduce a wire or fmall iron rod, to preferve a 



