118 WRITINGS OF JAMES SMITHSON. 



surfaces of them may be in the same plane ; and their dis- 

 tance is such that the needle when laid across them rests on 

 them at a small distance from the sides of the beam. They 

 rise above the surface of the table only one and a half or 

 two-tenths of an inch, so that the beam is very limited in 

 its play. 



The weights I use are one globule of gold, which weighs 

 one grain ; and two or three others which weigh one-tenth 

 of a grain each ; and also a number of small rings of fine 

 brass wire made in the manner first mentioned by Mr, 

 Lewis, by appending a weight to the wire, and coiling it 

 with the tension of that weight round a thicker brass wire 

 in a close spiral, after which the extremity of the spiral 

 being tied hard with waxed thread, I put the covered wire 

 in a vice, and applying a sharp knife which is struck with 

 a hammer, I cut through a great number of the coils at one 

 stroke, and find them as exactly equal to one another as can 

 be desired. Those I use happen to be the l-30th part of a 

 grain each, or 300 of them weigh 10 grains ; but 1 have 

 others much lighter. 



You will perceive that by means of these weights placed 

 on different parts of the beam, I can learn the weight of 

 any little mass from one grain or a little more to the Y^Vir 

 of a grain. For if the thing to be weighed weighs one 

 grain, it will, when placed on one extremity of the beam r 

 counterpoise the large gold weight at the other extremity, 

 If it weighs half a grain, it will counterpoise the heavy gold 

 weight placed at 5. If it weigh -^ of a grain, you must 

 place the heavy gold weight at 5, and one of the lighter 

 ones at the extremity to counterpoise it ; and if it weighs 

 only 1, or 2, or 3, or 4-100ths of a grain, it will be counter- 

 poised by one of the small gold weights placed at the first r 

 or second, or third, or fourth division. If on the contrary 

 it weigh one grain arid a fraction, it will be counterpoised 



