70 



of turns, making circles 12 centim. in diameter, then about 

 0-5 centim., further out another series, going on until the 

 last circle was 25 centim. These skeins, if they may be 

 so called, were suspended by silk threads within a light 

 wooden frame, and looked much like a spider's web ; and in 

 this way the wire was uninfluenced by the neighbourhood 

 of any wood or metal. The wire, however, had to be silk 

 covered and soaked in paraffine wax, and as both are bad 

 conductors of heat, it is evident that although the wire will 

 pretty quickly take the temperature of the air, yet greater 

 sensitiveness might be obtained. 



It would be difficult to have a satisfactory resistance of 

 uncovered wire with any other metal than platinum, and 

 this should be very fine, so as not to require too great a 

 length. I have, therefore, made another coil with 10 yards 

 uncovered platinum wire, about 004 millim. in diameter. 



^ First I put together a frame, something 



7y/ Z^///yy//yyy\ Hke a slate frame, and near and parallel 

 with the top and bottom fastened two 

 strings (35 centimetres apart) which 

 were threaded through small pieces 

 of tobacco pipe, fastened on with 

 shellac. The object of having a broken 

 up surface is to avoid connexion by 

 dew, or hoar frost. The platinum wire, 

 which is uncovered, is now led from 

 a piece of tobacco pipe on the upper 

 ^/ \//yyyyy/y////-f-al string round one on the lower, and up 



' — ' again to the second piece on the upper 



string, and thus from one to another until the whole is 

 fixed. In this way each wire is about 15 millim. from 

 the one before, and with this very fine wire we may, I 

 think, say that it will almost instantaneously take the 

 temperature of the air. The resistance is about 600 ohms, 

 and being wound so open does not, so far as the measure- 



