July 17, 1884] 



NA TURE 



285 



last few years by the introduction of argand burners, and globes 

 for the flat gas burners having much larger lower openings, so 

 that the dancing and flickering batswing burner of five years ago 

 is not so common in a good house. Even the steadiest of the 

 modern gas burners is extremely unsteady as compared with the 

 light of the incandescent electric lamp. Those of you who have 

 been to the Savoy Theatre will have noticed the effects of the 

 lights behind the scenes on the scenery itself. The light is so 

 absolutely steady that it is comparable to sunlight. Hitherto I 

 have said nothing as to the comparative excellence of the two 

 forms of electric light, viz. the electric arc and the incandescent 

 lamp. Both have their proper places. The arc light, which is 

 the whitest in colour and most economical to produce, is not so 

 steady as the incandescent lamp. It is therefore unsuitable for 

 indoor use or for reading by, or for such occupations as require 

 the maximum of steadiness. But it is well suited for the lighting 

 of large buildings and public places. I am unaware if any 

 experiments have been made as to the effects of brilliant arc 

 lighting on the eyesight of men who have to work night shifts, 

 as although the opinion of the workmen who have to work under 

 it is unanimous in its favour, yet that opinion is more based on 

 their personal comfort, due to their being able to carry on their 

 work with facility almost equal to that given by daylight. The 

 large sorting rooms at the General Post Office at Glasgow have 

 been for a long time lighted by the arc light, and with a most 

 beneficial result to the health and eyesight of the letter-sorters 

 and telegraph clerks. The former occupation is one which tries 

 the eyesight very severely. The public generally does not know 

 how the habit <>f writing the addresses on envelopes with pale 

 ink and blotting it off rapidly before it has time to darken tries 

 the eyesight of the Post Office letter-sorters. So long as 

 gas i 5 used, a powerful burner has to be brought very close 

 to the head of the sorter, and under such conditions the 

 eyesight fails at an early age. At Glasgow Post Office I am 

 able to boast that by the introduction of the electric light I 

 enabled many of the more aged sorters who were commencing 

 to use spectacles to do without them — and even I put back the 

 clock of time in enabling several who had used them for some 

 years to disclaim them. I am aware that it has been alleged by 

 the opponents of the electric light, whether interested or other- 

 wise, that in many cases the intensity of the light has injured 

 eyesight. I do not think any such cases can be substan- 

 tiated. Many of us who are in the habit of experimenting with 

 powerful arc lamps have had our eyelids temporarily affected by 

 incautious exposure at too short a distance. Again, over and 

 over I meet with the complaint that if I stare at an arc lamp for 

 a long time it will make my eyes ache ; the obvious retort being, 

 Why should you stare at the light ? If you do the same with the 

 sun, you will be equally inconvenienced. Before such an 

 audience as this, which is of course familiar with the beautiful 

 electric lighting in the Health Exhibition itself, it is useless for 

 me to enlarge on the many conditions of the electric light as it 

 indirectly affects health. I may only name the many addi- 

 tional pleasures of the eye we get from its use. Our flowers in 

 our rooms do not fade away, and are seen in their true colours. 

 Our pictures or all coloured objects are seen to better advantage. 

 I may mention one thing which would not generally occur to 

 you, that in London certainly an electric-lighted house can be 

 cleaned properly in winter. You may smile at this, but I assure 

 you that the advantage of being able to turn a flood of light into 

 your drawing-rooms and dining-rooms at six o'clock on a 

 winter's morning, so that the whole of the cleaning can be 

 finished as thoroughly as if done by daylight, before the family 

 comes down to breakfast, is one that must be experienced before 

 it can be thoroughly appreciated. Again, the advantage to the 

 health of our children is simply inestimable. No night-lights, 

 matches left about, or gas turned down low are required. A child 

 six years old can be trusted to press a button and so turn the light 

 off or on ; the lamps being high and out of reach are not easily 

 broken or over-turned, and the air of the children's nursery, 

 even if the light be kept burning the night through, remains pure 

 throughout. Another indirect advantage due to the absence of 

 heat is that it is comparatively easy to thoroughly ventilate and 

 cool during the hot weather a room lighted by the electric light. 

 The heat of gas placed high in the room causes such intense 

 draughts when the windows are open that the discomforts and 

 dangers of the draughts are almost worse than the discomfiture 

 from the heat and vitiated air, whereas in an electric-lighted 

 room there is no difficulty in opening wide all the windows, the 

 draughtsproduced being so gentle as to be hardly felt. 



SOCIETIES AND ACADEMIES 

 London 

 Physical Society, June 28.— Prof. Guthrie, President, in 

 the chair. — New Member, Mr. W. H. Hensley. — Lord Ray 

 leigh made a communication on the practical use of the silver 

 voltameter for the measurement of an electric current. On a 

 former meeting of the Society the method was explained by the 

 author, but on the present occasion the apparatus was exhibited. 

 The author considers this the best method of determining the 

 strength of current in absolute measure. One ampere deposits 

 4 grammes of silver in an hour ; therefore a quarter to half an 

 hour is sufficient to give 1 or 2 grammes, quantities which can 

 be measured with accuracy. Any current from 1/10 to 4 or 5 

 amperes can be measured successfully in this way. With very 

 weak currents there is a difficulty in weighing the deposits ; 

 with very dense currents the deposit is apt to be irregular. The 

 author deprecates the use of acetate of silver, pure nitrate or 

 pure chlorate of silver giving the best results. The cathode of 

 his apparatus is a platinum bowl, the anode a silver sheet 

 wrapped with clean filter paper sealed over it to keep any loose 

 silver from dropping on the cathode. The anode is immersed 

 in the solution of silver salt ; and at the end of several hours (if 

 great accuracy is required) a measurement of the weight of silver 

 deposited is made by weighing the bowl cathode in a chemical 

 balance. Dr. Fleming inquired whether it was not better to 

 weigh the loss of weight suffered by the anode, as is sometimes 

 done. Lord Rayleigh had not found this plan so good, the 

 anode being apt to disintegrate and lose weight, not by true 

 electrolytic action. Prof. Guthrie remarked that with small 

 electrodes peroxide of silver is formed, and that the inferiority 

 of acetate of silver might be due to formation of subacetate. — 

 Lord Rayleigh then made a communication on a colour-mixing 

 apparatus founded on refraction. This apparatus had been de- 

 scribed at a former meeting of the British Association, and con- 

 sists of a double-refracting prism, a lens, dispersing prism, and 

 screen, by which an overlapping of spectra can be obtained, and 

 thus a mixture of colours. In comparing different eyesights 

 with it Lord Rayleigh finds that the majority of persons are 

 more sensitive to red than he himself. In answer to Mr. W. 

 Baily he had not observed any difference between the two eyes 

 of the same person, except what might be due to fatigue and 

 freshness. Dr. Guthrie inquired if the author had discovered 

 any racial characteristics of colour-blindness. Lord Rayleigh 

 had not observed any so far. Dr. Guthrie stated that, though 

 colour-blind to red, he believed he was more than usually sensi- 

 tive to blue. Dr. Stone and Mr. Stanley referred to known 

 cases of blindness to green, as well as red. Dr. Lodge asked if 

 persons abnormally sensitive to red could see further down the 

 spectrum. Lord Rayleigh believed they could see the spectrum 

 brighter near its limits at all events. Mr. Glazebrook briefly de- 

 scribed a modification of Lord Rayleigh's apparatus by which the 

 distance on the spectrum which anyone can see could be measured. 

 — Mr. C. V. Boys read a paper on a phenomenon of electro- 

 magnetic induction. Between the poles of an electro-magnet 

 a small disk of copper is hung by a bifilar suspension. If the 

 magnetic field is uniform, and the disk at an angle to the lines of 

 force, then on making the magnet it is jerked parallel with the 

 lines of force. If it is a changing field, and the disk perpen- 

 dicular to the lines of force, it is repelled on making the magnet 

 and attracted on breaking by the nearest pole. This pheno- 

 menon, which was observed by Faraday, was shown by Mr. 

 Boys to be useful for determing the intensity of a magnetic field 

 by measuring the throw of the disk on magnetising and demag- 

 netising. It might also be employed to measure the resistance 

 of bodies in the form of plates, from their diameter, moment of 

 inertia, and observed throw. Any structural difference of resist- 

 ance in different directions in the body might be determined by 

 its means. Mr. Boys illustrated his remarks with curves of 

 results obtained by experiment. Lord Rayleigh considered that 

 the effect of self-induction on the results was not likely to be 

 serious. — Mr. J. Hopps read a paper on the alteration of elec- 

 trical resistance in metal wires produced by coiling and uncoiling. 

 His experiments were made with an inclined plane, the angle of 

 which could be varied, and a car, carrying bobbins, which was 

 drawn up or let down the plane by the wires experimented on. 

 It appeared that coiling and uncoiling tends to produce hard- 

 ness in a wire. Coiling produces an increase of resistance, and 

 uncoiling a decrease in the resistance of a wire. — Mr. R. T. 

 Glazebrook, M.A., F.R.S., read a paper on the determination 



