104 



SCIENCE. 



in the second, the electro-energy not converted into work, 

 diminishing with increase of speed, is converted into heat 

 in the conducting wire. The two causes are correlative. 



Let us cite a case having peculiar bearing on the trans- 

 mission of power at a distance by electro motors, for in- 

 stance, in electric traction on railways. Suppose our mo- 

 tor to turn at a normal speed developing a force of 70 

 volts. In this condition the work produced is repre- 

 sented (on the diagram) by A C, the work expended on 

 the source of electric supply by A H, and the return is 

 0.70. If the existing work is augmented (by putting on 

 a brake, for instance,) it will diminish the speed of the mo- 

 tor ; but the curve II. shows that by this very diminuilion 

 of speed the work produced by the motor augments, and a 

 new state ot equilibrium is produced very close to the first. 

 If, on the other hand, the resisting work diminishes, the 

 speed will augment, and the work produced will diminish. 

 Hence we see that the work of the motor augments with the 

 resistance, and diminishes as well with it, a most favor- 

 able condition for regulating speed and maintaining it 

 within certain bounds not far apart. This automatic gov- 

 erning is not to be found in any other motor. In the lat- 

 ter, special apparatus has to be called into play, as in the 

 well-known case of steam. 



This statement of the theoretical conditions affecting the 

 functions of an electro-motor supplied from a given source, 

 shows between what limits its different elements can be 

 made to vary. The numbers which we have given for the 

 maximum of work in batteries, as well as those given by 

 M. Reynier in his work on the pile, have regard only to the 

 total available energy in the external circuit, without con- 

 sideration of the manner in which this energy is ultimately 

 used. If, as in the above hypothetical case, it is desired to 

 transform this energy into work of an electio motor, but 

 half of the maximum work can be obtained. If, on the 

 other hand, it is proposed to get the greatest sum of work 

 in an indefinite time, the return can be augmented and col- 

 lected up to as high as 80 and 90 per cent, of the energy 

 represented by the expenditure of zinc in the battery, but 

 then the pile does not produce its maximum of work. 



The influences of the external resistances remain to be 

 examined, such as are presented in transmitting force at a 

 distance ; also the resistance of the motor itself, and the 

 practical returns obtained in certain special cases with mo- 

 tors of determinate type. 



We will take occasionjto recur to this subject after prac- 

 tical experience has had the last word. It is always well, 

 however, to recall theoretical results, which never being 

 altogether attained in practice, have an advantage in setting 

 exact limits to our knowledge of what can be obtained from 

 any given source of electrical supply ; and. while destroy- 

 ing some illusions, proving some statements, which till 

 now, have seemed too adventurous. (La Lumiere Electrique, 



Aug. 7th.) 



<•» 



MULTIPLE SPECTRA.* 



I concluded my last article under the above heading 

 w.th a reference to the case of carbon, and gave the results 

 successively arrived at by Attfield, Morren, Watts, and 

 others ; these went to show that besides the line-spectrum 

 of carbon mapped by Angstrom there exists a fluted spec- 

 trum of this substance. 



Now comes my own personal connection with this mat- 

 ter. 



In the year 1871,' I communicated to the Royal Society 

 a paper in which the conclusion was drawn that the vapor 

 of carbon was present in the solar atmosphere. 



This conclusion was founded upon the reversal in the 

 solar spectrum of a set of flutings in the ultra-violet.'- The 

 conclusion that these flutings were due to the vapor of car- 

 bon, and not to any compound ol carbon, was founded 

 upon experiments similar to those employed in the re- 

 searches of Attfield and Watts, who showed that the other 

 almost exactly similar sets of flutings in the visible part of 



•Continued from p. 29. ' 1'ro, . A'. .V. No. 187, 1878. 



3 The approximate wave-length of the brightest member on the least 

 rcfrangable edge is 3881.0. 



the spectrum were seen when several different compounds 

 of carbon were exposed to the action of heat and electricity. 

 In my photographs the ultra violet flutings appeared under 

 conditions in which carbon was the only constant, and it 

 seemed therefore reasonable to assume that the flutings 

 were due to carbon itself, and not to any compound of car- 

 bon, and this not alone from the previous work done in the 

 special case of carbon, but from that which had shown that 

 the fluted spectra of sulphur, nitrogen, and so forth, were 

 really due to these "elementary" substances. 



Professors Liveing and Dewar have recently on several 

 occasions called this result in question. Professor Dewar, 

 in a paper received by the Royal Society on January 8, 

 18S0, writes as follows: 



" The almost impossible problem of eliminating hydrogen 

 from masses of carbon, such as can be employed in experi- 

 ments of this kind, prove conclusively that the inference 

 drawn by Mr. Lockyer, as to the elementary character of 

 the so-called carbon spectrum from an examination of the 

 arc in dry chlorine, cannot be regarded as satisfactory, 

 seeing that undoubtedly hydrogen was present in the carbon 

 used as the poles. 



Subsequently, in a paper received by the Royal Society, 

 on February 2, Messrs. Liveing and Dewar wrote as fol- 

 lows : 



" Mr. Lockyer (Proc. Roy. Soc., vol. xxvii. p. 308) has re- 

 cently 3 obtained a photograph of the arc in chlorine, which 

 shows the series of fluted bands in the ultra-violet, on the 

 strength of which he throws over the conclusion of Ang- 

 strom and Thalen, and draws inferences as to the existence 

 of carbon vapor above the chromosphere in the coronal 

 atmosphere of the sun, which, if true, would be contrary to 

 all we know of the properties of carbon. We cannot help 

 thinking that these bands were due to the presence of a small 

 quantity of nitrogen." 



It will be seen that on January 8 Mr. Dewar alone at- 

 tributed the flutings to a hydrocarbon, while on February 2 

 Mr. Dewar, associated with Mr. Liveing, attributed them to 

 a nitrocarbon. 



In fact in the latter paper Messrs. Liveing and Dewar pub- 

 lished experiments on the spectra of various carbon com- 

 pounds, and from their observations they have drawn the con- 

 clusion that the set of flutings -vhich I have shown to be re- 

 versed in the solar spectrum is really due to cyanogen, and 

 that certain other sets of flutings shown by Attfield and 

 Waits to be due to carbon are really due to hydrocarbon. 



As Messrs. Liveing and Dewar do not controvert the very 

 definite conclusions arrived at by Attfield, Morren, Watts, 

 and others, I can only presume that they took for granted 

 that all the experimental work performed by these men of 

 science was tainted by the presence of impurities, and that 

 it was impossible to avoid them. I therefore thought it de- 

 sirable to go over the ground again, modifying the experi- 

 mental method so as to demonstrate the absence of impuri- 

 ties. Indeed I have started upon a research which will re- 

 quire some time to complete. Still, in the meantime, I have 

 submitted to the notice of the Royal Society some results 

 which I haveobtained, which I think settle the whole question, 

 and it is the more important to settle it as Messrs. Liveing 

 and Dewar have already based upon their conclusions theor- 

 etical views which appear to me likely to mislead, and which 

 I consider to have long been shown to be erroneous. To 

 these results I shall now refer in this place. 



The tube with which I have experimented is shown in Fig. 

 1 : a and 1: are platinum wires for passing the spark inside 

 the tube ; E is a small tube into which carbon tetrachloride 

 was introduced ; it was drawn out to a long narrow orifice 

 to prevent the rapid evaporation of the liquid during the ex- 

 haustion of the tube. The tube was benl upwards and a 

 bulb blown at c: in order that the spark might be examined 

 with the tube end-on, as its found that after the spark has 

 passed for some time a deposit is formed on the sides of the 

 bulb immediately surrounding the platinums, thus obstruct- 

 ing the light. After a vacuum had been obtained the tube 

 was allowed to icmain on the Sprcngcl pump, to which it 

 was attached by a mercury joint for the purpose of obtaining 

 a vacuum for a long time, in order that the last traces of air 

 and moisture might be expelled by the slow evaporation of 

 the liquid. 



3 That^is, in 1878.— J. N. L. 



