282 



NA TURE 



[July 17, 1884 



challenge my statement that the electric arc is yellow. It has 

 always been called a cold blue light. It is not so ; it is only by 

 comparison with the yellower light of gas or with the incan- 

 descent lamps that it appears blue ; when compared with the 

 sunlight reflected from a white cloud it will be seen to be dis- 

 tinctly yellow in tinge ; but still both classes of electric light are 

 far superior to all others in nearest approaching the white light 

 of daylight, and thus satisfying the actinic action which our 

 bodies demand. 



Turning now to the comparative heating and air-vitiating pro- 

 perties of artificial lights which we shall find it convenient to 

 take together, I have here a table (Table A) prepared by Dr. 



Table A. — Showing the Oxygen consumed, the Carbonic Acid 

 produced, and the Air vitiated, by the Combustion of certain 

 Bodies burnt so as to give the Light of 12 Standard Sp 1 in 

 Candles, each Candle burning at the rate of 120 grains per 

 hour 



Meymott Tidy, which shows the oxygen consumed, the carbonic 

 acid produced, the air vitiated, and the heat produced by the 

 combustion of certain bodies burned so as to give the light of 

 twelve standard candles, to which Mr. R. Hammond has added 

 the heat produced by a I2-candIe incandescent electric lamp. 

 From these figures you will see that the air of a room lighted 

 by gas is heated twenty times as much as if it were lighted to 

 an equal extent by incandescent electric lamps. When arc 

 lamps are used, the comparison is still more in favour of elec- 

 tricity. You will be surprised to see from the table that our old 

 friend the tallow candle, and even the wax candle, is far worse 

 than gas in the proportion of air vitiated and heat produced, and 

 you will be disposed to disbelieve it ; but the fact is, that so long 

 as candles were used light was so expensive that we were obliged 

 to l>e content with little of it ; in fact we lived in a state of 

 semi-darkness, and in this way we evaded the trouble. It is 

 only since the general introduction of gas and petroleum that we 

 have found what an evil it is. 



It is not unusual, in fact it is almost invariable, for us to find 

 the upper stratum of air of the rooms in which we live heated to 

 120° after the gas has been lighted for a few hours. We 

 have grown accustomed to this state of things, and are not 

 surprised that when we take the library ladder to get a bonk 

 from the upper shelf we find our head and shoulders plunged 

 into a temperature like that ofafurnace, producing giddiness and 

 general malaise. If you look again at the table you will see 

 that each gas burner that we use consumes more oxygen and 

 gives off more carbonic acid, and otherwise unfits more air for 

 breathing, than one human being, and it is this excessive heating 

 and air vitiation combined which are the main causes of the 

 injury to the health from working long hours in artificial light. 

 I could go on for a long time giving instances of the fearful state 

 of the atmosphere of our large public buildings as well as of our 

 private homes after the gas has been lighted for a few hours, but 

 this paper is not intended as an onslaught on gas ; moreover 

 these ills are so well known to nearly all of you that I need not 

 bring them more prominently before you. I will only take one 

 instance, viz. that of the Birmingham Town Hall, which has 

 been lighted alternately by gas and electricity. 



During the grand Birmingham Musical Festival, which was 

 held in that hall two years ago, some careful experiments were 



made to show how the orchestra and audience in the hall were 

 affected by the two kinds of lighting. The gas lighting was in 

 the form of several huge pendants suspended down the centre of 

 the hall. The electric lighting was in the form of clusters of 

 lights placed on large brackets projecting from the side walls 

 with two central pendants placed between the gas pendants. 

 The candle-power given by the electric light was about 50 

 per cent, in excess of that given by the gas light ; the 

 degree of illumination by electricity was consequently very 

 brilliant. 



It was found that when the gas was used the temperature near 

 the ceiling rose from 60° to IOO° after three hours' lighting. The 

 heating effect of the gas was, therefore, the same as if 4230 per- 

 sons had been added to the full audience and orchestra of 3100. 

 Similarly the vitiation of the air by carbonic acid was equal to 

 that given off by the breathing of 3600 additional persons added 

 to the above audience of 3100. But on evenings when the 

 electric light was used the temperature only rose ij° during a 

 seven hours' trial, and the air, of course, was only vitiated by 

 the breathing of the audience. The further experiment was 

 tried of giving to every member composing the large orchestra 

 a printed paper of questions asking how the new mode of 

 lighting affected him or her personally, and I have here 265 

 replies to those questions. They are very interesting. I will 

 read a very few of them out to you. From this you will learn 

 that without exception the comfort and general well-being of this 

 lai .,' orchestra was increased enormously by the use of the new 

 illuminant, yet it is reasonable to suppose that the comfort of the 

 audience was increased in an equal degree. Now we all ol us 

 know that the times when we suffer most from the effect of arti- 

 ficial light is in crowded places of public amusement, which are 

 at the same time brilliantly lighted. Many of us are unable to 

 go to the theatre or to attend evening performances of any kind, 

 intense headache which invariably attends through staying 

 le hour in such places entirely prevents them. This head- 

 commonly say is inseparable from the heat and glare ol 

 the gas. Now this phrase is not strictly correct. It is no doubt 

 due to the heat of the gas and its air-vitiating properties, but 

 when we use the word glare I believe we rein to the effect the 

 gaslight has upon our heads, and which effect is not due to 

 excess of light. On the contrary, I believe if a far greater 

 amount of light tie given by the electric light without the heating 

 and air vitiation being present such headache is never produced, 

 although some of the more tender-headed amongst us will at 

 first complain of the glare because they are habituated to .1 ii 1 

 ciate plenty of light with great heat, great air vitiation, and 

 other evils. 



Indeed, so long have we been accustomed to closely asso- 

 brilliant artificial light with headache and glare, that we 

 who are introducing electric light are most cautious not to give 

 the full quantity of light which we could afford to give, and 

 which would afford the greatest rest to the eye and greatest 

 bodily comfort. I now come to the effect that light has upon 

 the temperament. If we try the experiment in an assemblage 

 of people of gently decreasing the lighting of the room, it will 

 be found that the spirits of every one will be depressed just as 

 the light is depressed, and, vice versa, their spirits will tie raised 

 just a, the light is raised. I have many times, when conducting 

 experiments of electric lighting on a large scale, noticed this 

 fact, and I have been led to the conclusion that during hours of 

 waking every p rum is benefited by increase of Hole' up to the t.x- 

 len! of ful! sunlight, providing that this high degree of lighting 

 is ii"i attended by heat and by air vitiation; and I must add 

 that the source of light must not be from one or two brilliant 

 points only, but it must be well regulated and not such as to 

 dark, deep shadows. 

 This leads me on to the subject of the effects on the eyesight 

 of the electric light as compared with other light-. Healthy 

 '. mands a plentiful supply of light. It is t'i 



appose that a state of semi-darkness is good for our 

 eyes, unless they are defective, or recovering from the effects of 

 past injury or disease. Whoever saw a painter, engraver, 

 printer, watchmaker, or indeed any one the quality of whose 

 work depends on the excellence of his eyesight, who did not 

 desiie a Hood of pure white light thrown on to his work. I 

 think I have the authority of oculists when I say that I9-20ths 

 of the diseases of the eyes arise from working the eyesight long 

 hours with insufficient light. Again, another great cause of 

 injury to eyesight is the unsteadiness of most artificial lights. 

 Much improvement has been made in the light of gas during the 



