WRITINGS OF JAMES BMITUSON. 119 



by the heavy gold weight at the extremity, and one or more 

 of the lighter ones placed in some other part of the beaip. 



This beam has served me hitherto for every purpose ; but 

 had I occasion for a more delicate one, I could make it 

 easily by taking a much thinner and lighter slip of wood, 

 and grinding the needle to give it an edge. It would also 

 be easy to make it carry small scales of paper for particular 

 purposes. 



We have no chemical news. I am employed in examin- 

 ing the Iceland waters, but have been often interrupted. I 

 never heard before of the quartz-like crystals of barytes 

 aerata, nor of the sand and new earth from New Holland. 

 Indistinct reports of new metals have reached us, but no 

 particulars. Some further account of these things from 

 you will, therefore, be very agreeable. Dr. Hutton joins 

 me in compliments, and wishing you all good things ; and I 

 am. Dear Sir, 



Your faithful humble servant, 



Joseph Dlack. 



Note by Mr.SMiTHSON. — The rings mentioned above have 

 the defect of their weight being entirely accidental ; and 

 consequently most times very inconvenient fractions of the 

 grain. I have found that a preferable method is to ascertain 

 the weight of a certain length of wire, and then take the 

 length of it which corresponds to the weight wanted. If 

 line wire is employed, a set of small weights may be thus 

 made with great accuracy and ease. Inconvenience from 

 the length of the wire in the higher weights is obviated by 

 rolling it round a cylindrical body to a ring, and twisting 

 this to a cord. 



This little balance is a very valuable addition to the blow- 

 pipe apparatus, as it enables the determination of quantities 

 in the experiments with that instrument, which was an un- 

 hoped-for accession to its powers. 



Dr. Black mentioned to me its having been used by an 



