1866.] Electricity given hy Induction-Machines. 



181 



components, though K has only half as many spires as G and but a tenth 

 of its resistance. 



In combining these instruments, the primaries should not be consecutive 

 if of large numbers, for so the action of their extra-current would be very 

 destructive to the rheotome ; with P' + P" containing 726 spires in series 

 the spark in the mercurial one is almost explosive, but when they are 

 collateral it works quietly. Were, however, ten or twelve to be so com- 

 bined, it would require a battery of very large cells to maintain the cur- 

 rent, and it is better to have a separate battery for each pair of primaries. 

 In this I find no difficulty ; the negative * poles of all the batteries are 

 connected with the mercury of the rheotome ; from its platinum point, 

 separate wires go to the entering bind-screw of each primary, other wires 

 go from their exit bind-screws to the positive poles of their respective bat- 

 teries, and thus their action is perfectly simultaneous. Of course, if many 

 batteries were used, the current in the rheotome might be too powerful, 

 but then there would be no difficulty in having separate rheotomes worked 

 by one electromagnet, and (at least with the mercurial form) adjusting 

 them by a revolving mirror to perfect synchronism. 



In this way I feel sure that we can attain an amount of electric power 

 which has not yet been approached by the inductorium, and which may 

 be expected to be a most powerful means of research in those inquiries to 

 which I referred at the commencement of this paper. At the head of 

 these stands the palmary discovery of Mr. Huggins, that there are nebulae 

 and comets whose matter possesses spectral attributes not corresponding 

 to that of the sun, the stars, or our own earthly elements. Is that differ- 

 ence an indication of some body sui generis, or a mere result of peculiar 

 temperature or other molecular conditions 1 Is, for instance, the bright 

 line, corresponding to one of nitrogen, which occurs, we may say, normally, 

 produced by nitrogen as such? If so, what has blotted out the other 

 bright lines of that magnificent spectrum ? Is it due to an element of 

 nitrogen, dissociated by some enormous temperature from other elements, 

 perhaps from hydrogen, one line of which is also present 1 And the third 

 line, elsewhere unknown — is it the herald of a new body, or merely a deri- 

 vative from another spectrum ? We cannot even hope for an answer to 

 these questions till the spectra of at least those elements which seem cos- 

 mical have been examined through a range of temperature extending from 

 the lowest that developes in them luminous lines, to the highest that is 

 excited by the most potent electric discharges which we can produce and 

 control. Now, to obtain such a graduated range, the plan of combination 

 which I have been describing seems well fitted. It, of course, cannot be 

 expected to equal, under any extension, the wonderful voltaic battery of 

 Mr. Gassiot (at least its arc-discharge) ; but how few can avail themselves 



* If the mercury be made positive, each discharge makes a sharp report and blows 

 about the metal and alcohol in most unpleasant profusion. 



