SCIENCE. 



493 



case of currents going in parallel and in opposite direc- 

 tions. 



The theory is carried out a step further to explain the 

 attraction and subsequent repulsion after contact of an I 

 electrified and a neutral substance and the passage of a 

 spark. But it is extremely speculative, and is not as yet 

 experimentally illustrated, and I think that at present it 

 is better to pass it by, 



I believe that the professor will exhibit his experiments 

 and give some account of his mathematical investigations, 

 which have occupied his time for five years, to the Aca- 

 demie des Sciences this afternoon. His results have not 

 been published before. George Forres. 



THE ELECTRIC DISCHARGE THROUGH 

 COLZA OIL.* 

 By A. Macfarlane, D. Sc., F. R. S. E. 



The electrical properties of colza oil which I have ex- 

 amined are its dielectric strength and some phenomena 

 which accompany the passage of the spark. By the di- 

 electric strength of a substance I mean the ratio of the 

 difference of potential required to pass a spark through 

 air under the same conditions. The electrodes used were 

 two parallel brass plates each four inches in diameter. 

 When comparing the gases the standard distance of the 

 plate chosen was 5 mm. In the case of liquids it is con- 

 venient to observe for a shorter distance, and reduce the 

 result by the law which previous experiments of mine 

 have established, namely, that in the case of the dis- 

 charge between parallel plates through a liquid dielectric, 

 the difference of potential required is proportional to the 

 distance between the plates. (Trans. R. S. E., vol. xxix. 

 p. 563). One set of observations gave the ratio for colza 

 oil to be 2.7, another gave 2.5. Hence 2.6 may be taken. 

 I have now obtained the following table of dielectric 

 strengths for'liquids (1 being unity). 



Substance. Dielectric Strength. 



Paraffine oil 3.7 



Oil of turpentine 4.0 



Paraffine liquefied 2.4 



Olive oil 3.5 



Colza oil 2.6 



The specific gravity of the colza oil is .91. The passage 

 of the spark was accompanied by the formation of gas 

 bubbles, but there was no deposition of solid particles. 

 As the 4-inch plates were placed horizontally in the oil a 

 bubble produced by the discharge was prevented from 

 escaping by the upper plate. When the upper plate is 

 again electrified such a bubble behaves in the following 

 manner. If it is large enough it will extend itself some- 

 what like an hour-glass between the plates, but if it is 

 smaller it takes the form of an acorn with a flat base, the 

 base resting on one or other of the plates. When the 

 upper plate is charged positively the bubble is repelled 

 so as to place its base on the lower plate ; when the elec- 

 tricity is changed to negative the bubble remains with its 

 base on the upper plate. A reversal of the order of 

 charging did not change the effect. After a few electri- 

 fications a sufficient number of solid particles collect to 

 form a chain, and thus interfere with the phenomenon, 

 the bubbles then being lengthened out in a remarkable 

 manner, but never repelled to the lower plate. When 

 the upper plate was charged negatively, gas bubbles ap- 

 peared to me to rise from the lower plate, as if they had 

 been formed there. To test this point further I took 

 some sparks between two smaller disks placed vertically 

 in the oil. The gas-bubbles were observed to rise up at 

 the negative surface as if they had been formed at the 

 positive surface, and had been repelled or carried straight 

 across, and then rose up at the negative surface. When 

 the spark was taken between two points bent at right 



angles to two rods dipping into the oil, the bubbles were 

 observed to shoot out in the direction from the positively 

 charged point, and to circulate round the earth-rod some 

 1 time before rising to the surface. These phenomena in- 

 dicate that the bubble is positively electrified. 



ASTRONOMY. 

 ON THE POSSIBILITY OF THE EXISTENCE OF INTRA- 

 MERCURIAL PLANETS.* 

 By Balfour Stewart, LL.D., F.K.S. 



It is a somewhat frequent speculation amongst those 

 who are engaged in sun-spot research to regard the state 

 of the solar surface as influenced in some way by the 

 positions of the planets. 



In order to verify this hypothesis observers have tried 

 whether there appear to be solar periods exactly coin- 

 ciding with certain well-known planetary periods. This 

 method has been adopted by the Kew observers (Messrs. 

 De La Rue, Stewart, and Loewy), who had an unusually 

 large mass of material at their disposal, and they have 

 obtained from it the following results : — ■ 



1. An apparent maximum and minimum of spotted 

 area approximately corresponding in time to the peri- 

 helion and aphelion of Mercury. 



2. An apparent maximum and minimum of spotted 

 area approximately corresponding in time to the conjunc- 

 tion and opposition of Mercury and Jupiter. 



3. An apparent maximum and minimum of spotted 

 area approximately corresponding in time to the conjunc- 

 tion and opposition of Venus and Jupiter. 



4. An apparent maximum and minimum of spotted 

 area approximately corresponding in time to the conjunc- 

 tion and opposition of Venus' and Mercury. 



The Kew observers make the following remarks upon 

 these results : — 



" There appears to be a certain amount of likeness 

 between the march of the numbers in the four periods 

 which we have investigated, but we desire to record this 

 rather as a result brought out by a certain specified 

 method of treating the material at our disposal than as a 

 fact from which we are at present prepared to draw con- 

 clusions. As the investigation of these and similar phen- 

 omena proceeds, it may be hoped that much light will 

 be thrown upon the causes of sun-spot periodicity. 



The Kew observers have likewise produced evidence 

 of a different kind in favor of the planetary hypothesis, 

 for they have detected a periodicity in the behavior of 

 sun-spots with regard to increase and diminution appar- 

 ently depending upon the positions of the two nearer 

 planets, Mercury and Venus. I The law seems to be 

 that as a portion of the sun's surface is carried by rota- 

 tion nearer to one of these two influential planets, theie 

 is a tendency for spots to become less and disappear, 

 while on the other hand, when it is carried away from 

 the neighborhood of one of these planets, there is a ten- 

 dency for spots to break out and increase. 



But whatever truth may be in these conclusions, it 

 appears to be quite certain that periodical relations be- 

 tween the various known planets will not account for all 

 the sun-spot inequalities with which we are acquainted. 

 They may account for some, but certainly not for all. 

 For there are solar inequalities of short duration which 

 presuming tht;m to be real, can only be accounted for on 

 the planetary hypothesis, by supposing the existence 01 

 several unknown intra-Mercurial planets. 



Indeed these short-period inequalities in sun-spots and 

 the allied phenomena of terrestrial magnetism and me- 

 teorology have so augmented in number of late years as 

 to make some observers inclined to question their reality; 

 whils others again resort to the above-mentioned hypo- 

 thesis, and attribute them to intra-Mercurial planetary 

 agency. 



The method to be pursued in detecting the existence 



* British Association, 1881. 



British Association, 1881. 



