October 12, 1888.] 



SCIENCE. 



173 



ing, are highly probable : certainly they do not arise from contact 

 with the natural oils of the heavier gravities, viz., 26° B. to 35° B. 

 The Value of Vaccination. —Zurich, according to The 

 Laticet, is beginning to suffer from the effects of neglect of vac- 

 cination. Until 1883 a compulsory vaccination law was in force, 

 but in that year it was repealed ; the success of the anti-vaccina- 

 tionists depending, it is said, upon the fact that not a single case of 

 small-pox occurred in 1882. But in 1883, in every 1,000 deaths, 2 

 were caused by small-pox; in 18S4 there were 3 in every 1,000; in 

 1885, 17; and in the first quarter of 1886 there were 85 deaths. 

 While Europe is exhibiting folly by showing in some localities op- 

 position to vaccination, Japan is deriving benefits from the recog- 

 nition of its value. Nagasaki possesses a governor, named Kusaka, 

 who is bent upon ridding the town of the diseases which formerly 

 infested it. By means of a system of compulsory vaccination, 

 rigorously enforced by the governor, small-pox, long a familiar 

 scourge in the old town, has been practically stamped out. Ger- 

 many, too, is showing the effects of revaccination, and hitherto the 

 freedom of German towns from small-pox has contrasted in a 

 marked degree with a larger prevalence of this disease in other 

 European towns where revaccination is not enforced. Probably 

 the outcome of the experience of the present generation will be the 

 ■enforcement of revaccination in the majority of civilized countries. 



The Tudor Accumulator. — Some details of tests of the 

 Tudor accumulator have already been given in this journal, but the 

 following data are more complete than any hitherto obtainable. 

 In the Tudor accumulators a crystalline coating of peroxide of lead 

 is formed on the positive plates by a process that lasts two or three 

 months, while the negatives are produced by the application of red 

 lead, as in the ordinary types. Two of these cells, said to have 

 been in use from November, 1 881, to December, 1887, were tested 

 by Prof. W. Kohlrausch. They were submitted to thirty-four 

 charges and thirty-four discharges, there being a mean interval 

 between the two of fifteen hours. The weight of the plates in a 

 cell is 13.6 kilograms; the volume of the liquid, 3,4 litres ; there are 

 four positive plates with a surface of 12 square decimetres; the 

 normal charging current is 5 amp&res; discharge current, 6.5 am- 

 peres. The following figures give some results of the tests : — 



ELECTRICAL SCIENCE. 

 Is the Velocity of Light in an Electrolytic Fluid influenced 



by an Electric Current in the Direction of Propagation ? 



The following description of Lord Rayleigh's experiment on this 

 subject is given in Professor Lodge's sketch of the papers read be- 

 fore the last meeting of the British Association : — 



It is well known, that, when an electric current flows through an 

 ■electrolyte, an actual transfer of matter accompanies it, — two op- 

 posite transfers, in fact, as evidenced by the continuous appearance 

 and escape of the travellers, one at each electrode. It is also 

 known by a refined experiment of Fizeau, confirmed by Michelson, 

 that, when a beam of light travels down a stream of moving matter, 

 its velocity is slightly increased ; whereas, if light travels against a 

 stream of matter, it is slightly retarded. These things being so, it 

 may be held as probable, that, whenever the two ions taking part 

 in an electrolytic current differ in momentum, a slight effect may be 

 exerted on the velocity of light travelling with or against the cur- 

 rent ; but then, according to the calculations of Kohlrausch, con- 

 firmed by some experiments of Professor Lodge, the speed of the 

 electrolytic ions is extremely small, the quickest being thirty 

 microns per second, or about four inches an hour, for an applied 

 slope of potential of one volt per centimetre. 



The effect of such a creep as this was not what Lord Rayleigh 

 looked for. It was quite within the range of possibility that the 

 existence of an electric current in an electrolyte should so disturb 

 the ether inside it as to produce quite a notable change in its index 

 of refraction. Were such an effect discovered, it would be a dis- 

 tinctly new fact, not taken into account, or even rendered probable, 

 by existing theories ; and it is very well to have the question exper- 

 imentally examined, and to a certain extent set at rest. 



The method adopted was a beautiful interference arrangement 

 ■of Michelson, whereby a beam of light is split up into two halves, 

 which are sent along a certain route, or circular tour, and are then 

 recombined into one at the point whence they originally split off, 

 and are examined by a magnifying eye-piece. The result is a set 

 of interference-bands more or less well defined. Tubes containing 

 dilute sulphuric acid supplied with an electric current are then 

 placed along the route taken by the two half-beams of light, so that 

 one half the beam will be helped and the other half hindered by the 

 current, if it produce any effect at all. The thing looked for is to 

 see if the interference-fringes shift along microscopically when the 

 ■current is supplied, stopped, or reversed. The result is negative; 

 and, by considering carefully how much of an effect could have 

 been certainly perceived if it had existed, the definite statement is 

 made, that a current of intensity of one ampere per square centmietre 

 through dilute sulphuric acid does not affect the velocity of light in 

 its own direction by so much as one part in thirteen million, or by 

 ■fifteen metres per second. 



The following figures are also of value in comparing with other 

 types of secondary batteries : — 



Density of liquid 



Internal resistance 



Current density per square decimetre 



Capacity in ampere hours per kilogram of pU 

 Capacity in watt hours per kilogram of plate 



Discharged. 



Let us compare the capacity and discharge-rate of this cell with a 

 Julien cell, the weight of the plates being about the same. The 

 figures given for the Julien cell are approximate. 



Useful capacity (watt) 



Discharge-rate 



Efficiency 



The Tudor accumulator is, then, inferior to the well-known ' grid 

 type ' in storage-capacity and discharge-rate, — two very important 

 factors. Its greater efficiency is partly due to the low discharge- 

 rate. As far as length of life and ability to resist rough usage go, 

 the Tudor cell is, if we are to believe the report, superior. The 

 cells under test were said to have been in use for si.x years, and 

 were in good condition. During the experiments they were several 

 times allowed to become completely discharged — an operation that 

 severely injures an ordinary' cell — without apparent ill effect ; and 

 once the cells were completely reversed, and then charged again in 

 the right direction, still without apparent injury. In considering 

 the value of new types of accumulators, the main points to be con- 

 sidered are, leaving out questions of first cost, discharge-rate, 

 length of life, storage-capacity, and ability to resist rough usage. 

 In length of life and ability to resist rough usage the Tudor bat- 

 teries seem to give better results than any for which reliable figures 

 have been given. In storage-capacity and discharge-rate they are 

 distinctly inferior to the ordinary type ; and it is these defects, 

 especially the latter, that render them unfit for traction-work, and 

 for most cases of central-station lighting. 



