TRANSACTIONS OF THE SECTIONS. 19 



tlie other (the receiver-spring') with an insulated piece of metal called the receiver, 

 which is analogous to the " prime conductor " of an ordinary electric machine. 

 The point of contact of the earth-spring with the carriers is exposed to the in- 

 fluence of an electrified hody (generally an insulated piece of metal) called the in- 

 ductor. When this is negatively electrified, each carrier comes away from contact 

 with the earth-spring, carrying positive electricity, which it gives up to the re- 

 ceiver-spring. The receiver and inductor are each hollowed out to a proper shape, 

 and are properly placed to surround, each as nearly as may be, the point of contact 

 of the corresponding spring. 



The inductor, for the good working of the machine, should be kept electrified to 

 a constant potential. This is effected by an adjunct called the replenisher, which 

 may be applied to the main wheel, but which, for a large instrument, ought to be 

 worked by a much smaller carrier- wheel, attached either to the same or to another 

 turning shaft. 



The replenisher consists chiefly of two properly shaped pieces of metal called 

 inductors, which are fixed in the neighbourhood of a carrier-wheel, such as that 

 described above, and four fixed spriugs touching the carriers at the ends of two 

 diameters. Two of these springs (called receiver-springs ) are connected respectively 

 with the inductors ; and the other two (called connecting springs) are insulated 

 and connected with one another. They are so situated that they are touched by 

 the can-iers on emerging from the inductors, and shortly after the contacts with the 

 receiver-springs. If any ditt'erence of potential between the inductors is given to 

 begin with, the action of the carriers, as is easily seen, increases it according to the 

 compound interest law as long as the insulation is perfect. Practically, in a few 

 seconds after the machine is started running, bright flashes and sparks begin to 

 fly about in various parts of the apparatus, even although the inductors and con- 

 nectors have been kept for days as carefidlj' discharged as possible. The only in- 

 strument yet made is a very small one (with carrier-wheel two inches in diameter) 

 constructed for the Atlantic Telegraph application ; but its action has been so 

 startlingly successfid that great eflects may be expected from larger machines on 

 the same plan. 



"When this instrument is used to replenish the charge of the inductor in tlie 

 con.<tant electric machine, described above, one of its inductors is connected 

 with the earth and the other with the inductor to be replenished. "Wlien accurate 

 coustancj' is desired, a gauge-electroscope is applied to break and make contact 

 between the coimector springs of the replenisher when the potential to be main- 

 tained rises above or falls below a certain limit. 



Several usefurapplications of the replenisher for scientific obsen'ation were shown ; 

 among others, to keep up the charge in the Lejden jar for the divided-ring mirror- 

 electrometer, especially when this instrument is used for recording atmospheric 

 electricity. A small replenisher, attached to the instrument within the jar, is 

 worked by a little milled head on the outside, a few turns of which suffice to re- 

 plenish the loss of twenty -foiu' hours. 



Meteoeologt. 



Notice respecting a Haj/stach strucJc hy LiffJitninij. 

 Bij Sii- David Erewsteb, K.H., LL.D., F.R.S. 

 The author gave an account of the production of a substance found at the bottom 

 of a circidar passage made by a lightning stroke in a stack of hay at Dun in For- 

 farshire in 18:^7. The specimen, which was produced from the silex in the hay, 

 had a gTeenish tinge, and contained portions of burnt hay. It has been deposited 

 in the Museum of St. Andrews. 



Ohservcitions of the Rainfall at Arhroath. Bi/ Alexander Brown. 



2* 



