On dividing Instruments. J 63 



produces the smallest effect of all, and does but little good 

 or harm. 



Secondly, If it enters the body by a conductor in contact, 

 and has to e^capt- in the manner of perspiration, a strong 

 effect is produced ; and ihis may be confined to one place, 

 and of course be rendered more powerful by the attracting 

 points 



Thirdly, An effect equallv strong, but quite the reverse 

 of the last, will l)e produced bv placmgthe patient insulated 

 in contact aith the negative conductor, and in a damp at- 

 mosphere *. Bv this mode of operating the effect takes 

 place all over his body : but if, instead of this, you bring a 

 wet spfJUtje, connected with the earthy near the part affected, 

 it will be confined to that place. 



- In the forn)er case the electricity acts by increasing the 

 natural persj>ira;ion8j but in the latter, by strongly checking 

 it, or occasioning an absorption of moisture. 



I think the failures in medical electricity have been where 

 this last application was wanted ; for electricity alone, ap- 

 plied in any way, has a tendency to dissipate moisture j 

 which cff'ect the last inethod enables you to reverse. 



' P;id<Jiu^a:ton, Aug. 3, 1809. 



XXIV. ^n Jccount of a Method of dividing astronomical 

 and other hutrument'i^ by ocular Inspection ; i« ii'hich 

 the usual Tools for graduating are not employed ; tile 

 whole Operation, beina so contrived, that no Error can oc- 

 cur but what is chargeable to Vision, ivhen as isted by the 

 best optical Means of viewing and measuring minute 

 Quantities. By 3/r. Edwahjj Troughton. 



[Concluded from p. 03.] 



JlVespecting the angular value of the numbers in these 

 tables, it may be worth mentionine, that it is not of the 

 least importance; !()() of them being comprised in one re- 

 volution of the micrometer screw ; and, in the instance 

 before me, 5'6 of them made no more than a second. Il 

 is not pretended that one of these parts was seenbeyond a 

 d(nibt, being scarcely ■s-T^-cnr^h of an inch, much less the 

 tenths, as exhibited in the tables ; but, as they were visible 

 upon the micrometer heads, it was judged best to take them 

 into the account. 



• A damp atmosphere is easily produced by usiug a pan of hollin^ water ; 

 but in tliis caw the machine, that it may t)e Icept dry, should be in Jtriothcr 

 runm, aad (he cwodactov thoulU p<i»s, insulated, through Lite wall to the 

 pa (lit. 



L 2 Having 



