July 17, 1884] 



NA TURE 



281 



purple, and purplish red. Clear yellow, and all shades of green 

 and blue colours, are rarely, if ever, met with. These facts in- 

 dicate that the deep sea is illuminated only by the sea-green 

 sunlight that has passed through a vast stratum of water, and 

 therefore lost all the red and orange rays by absorption. The 

 transmitted rays of light could not be reflected by the animals 

 referred to, and therefore they would be rendered invisible. 

 Their bright colours can only become visible when they are 

 brought up into the white sunlight. These bright colours are 

 therefore just as much protective as the dull and black colours of 

 other species. 



The deep-sea star-fishes are nearly all orange, orange-red, or 

 scarlet, even down to three thousand fathoms. The larger 

 ophiurans are generally orange, orange-yellow, or yellowish 

 white, the burrowing forms being usually whitish or mud- 

 coloured, while the numerous species that live clinging to the 

 branches of gorgonians and to the stems of Pennatulacea are 

 generally orange, scarlet, or red, like the corals to which they 

 cling. Among such species are Astrochele lymani, abundant on 

 the bushy orange gorgonian coral, Acanella normani, often in 

 company with several other orange ophiurans belonging to 

 Ophiacantha, &c. Astronyx loveni and other species are com- 

 mon on Pennatulacea, and agree very perfectly in colour with 

 them. These, and numerous others that might be named, are 

 instances of the special adaptations of colours and habits of com- 

 mensals for the benefit of one or both. Many of the large and 

 very abundant Actinia;, or sea-anemones, are bright orange, red, 

 scarlet, or rosy in their colours, and are often elegantly varied 

 and striped, quite as brilliantly as the shallow-water forms ; and 

 the same is true of the large and elegant cup-corals, FlaMlum 

 °oodei, F. annulare, and Caryophyilia communis, — all of which 

 are strictly deep-sea species, and have bright orange and red 

 animals when living. The gorgonian corals of many species, 

 and the numerous sea-pens and sea-feathers (Pennatulacea), 

 which are large and abundant in the deep sea, are nearly all 

 bright coloured when living, and either orange or red. All these 

 Anthozoa are furnished with powerful stinging organs for offence 

 and defence ; so that their colours cannot well be for mere pro- 

 tection against enemies, for even the most ravenous fishes seldom 

 disturb them. It is probable, therefore, that their invisible colours 

 may be of use by concealing them from their prey, which must 

 actually come in contact with these nearly stationary animals in 

 order to be caught. But there is a large species of scale-covered 

 annelid (Polyno,- aurantiaca, Verr.) which lives habitually as a 

 commensal on Bolocera tiiedui, a very large orange or red 

 actinian, with unusually powerful stinging organs. Doubtless 

 the worm finds, on this account, perfect protection against fishes 

 and other enemies. This annelid is of the same intense orange 

 colour as its actinian host. Such a colour is very unusual among 

 annelids of this group, and in this case we must regard it as 

 evidently protective and adaptive in a very complex manner. 



It has been urged by several writers, that the light in the deep 

 sea is derived from the phosphorescence of the animals them- 

 selves. It is true that many of the deep-sea Anthozoa, hydroids, 

 ophiurans, and fishes are phosphorescent ; and very likely this 

 property is possessed by members of other groups in which it 

 has not been observed. But, so far as known, phosphorescence 

 is chiefly developed in consequence of nervous excitement or 

 irritation, and is evidently chiefly of use as a means of defence 

 against enemies. It is possessed by so many Anthozoa and 

 acalephs which have, at the same time, stinging organs, that it 

 would seem as if fishes had learned to instinctively avoid all 

 phosphorescent animals. Consequently it has become possible 

 for animals otherwise defenceless to obtain protection by ac- 

 quiring this property. It is well known to fishermen that fishes 

 avoid nets, and cannot be caught in them, if phosphorescent 

 jelly-fishes become entangled in the meshes ; therefore it can 

 hardly be possible that there can be an amount of phosphorescent 

 light, regularly and constantly evolved by the few deep-sea 

 animals having this power, sufficient to cause any general illu- 

 minate in, or powerful enough to have influenced, over the whole 

 ocean, the evolution of complex eyes, brilliant and complex 

 protective colours, and complex commensal adaptations. 



It seems to me probable that more or less sunlight does actually 

 penetrate to the greatest depths of the ocean in the form of a 

 .-•oft sea-green light, perhaps at two thousand to three thousand 

 fathoms equal in intensity to our partially moonlight nights, and 

 possibly at the greatest depths equal only to starlight. It must 

 be remembered that in the deep sea, far from land, the water is 

 far more transparent than near the coast. A. E. Verrill 



ARTIFICIAL LIGHTING ' 



TN early times but a small fraction of our forefathers' lives was 

 spent under artificial light. They rose with the sun and lay 

 down to rest shortly after sunset. During the long winter 

 evenings they sat round the fire telling stories and singing songs 

 of love and war ; the fire-light was sufficient for them, except 

 occasionally during grand feasts and carousals, when their halls 

 were lighted by pine-wood torches or blazing cressets. But, as 

 a rale, after sunset they lived in semi-darkness. 



From that early period, as man has advanced in civilisation, 

 in the thirst for knowledge derived from books, and in following 

 the gentler pursuits which demand an indoor life, there has been 

 a steady increase in that fraction of our lives which is spent 

 under light other than that of the sun. But the improvement in 

 the quality of the artificial light has been very slow. The ruddy 

 lights and picturesque shadows so faithfully handed on to us by 

 Rembrandt's pictures show us very graphically what our poets 

 have called "the dim glimmer of the taper" of those days. A 

 few years before the introduction of gas, Argand, by his im- 

 provements in the burners of oil lamps, enabled our fathers to 

 see for the first time a comparatively white light,- but as far as 

 the matter we to-day propose to discuss is concerned, viz. the 

 effect of artificial lighting, and more particularly electric lighting, 

 on _ our health, we need only consider the reign of artificial light 

 as it commenced with the general use of gas and petroleum, for 

 then and only then could it be said to affect our health. 



Prior to the introduction of the electric light we have been 

 accustomed to consider every hour spent under artificial light as 

 an hour during which all conditions are less favourable to per- 

 fect health than they would be during daylight. Can we now 

 hope to ameliorate this condition of things through the agency of 

 electricity ? Before we can discuss this question I must point 

 out to you the chief differences which exist between hours of 

 work or recreation spent in daylight and under artificial light. 

 In the former case we live in abundance of light. The sunlight 

 itself exercises a subtle influence on our bodies ; that mixture of 

 heating and chemical rays which when analysed form the solar 

 spectrum, and combined form the pure white light 'of daylight, 

 is needed to enable all animal and vegetable organisms to 

 flourish in the fullest conditions of healthful life. 



In nearly all cases when the sun is up, the functions of life are 

 in the state of fullest activity, and when it sets they sink into 

 comparative repose. In daylight life wakes, in darkness life 

 sleeps. In addition to the abundance of pure white light, the 

 heat attending is only that necessary for health. The air re- 

 mains unvitiated, except by our own breathing. On the other 

 hand, when working under artificial light, we have these condi- 

 tions all altered in degree : 



1. We have an insufficient light ; a scale of lighting by gas 

 or by electricity which would be pronounced excessive at night- 

 time is still far inferior to average daylight. 



2. All artificial lights, whether produced by combustion, as in 

 the case of candles, oil, gas, and petroleum, or by the incan- 

 descence of a conductor by the means of electricity, produce 

 heat ; this heat, in proportion with the light afforded, is enor- 

 mously in excess of the heat given by sunlight. Electricity, as 

 you will see hereafter, is far the best in this respect, but even it 

 is inferior to sunlight. 



3. All these same illuminants, excepting electricity, contamin- 

 ate the air and load it with carbonic acid, sulphur, and other 

 compounds — all injurious to the health and to the general com- 

 fort of the body. It will be convenient to consider the effects 

 —first, on our health generally ; second, on our eyesight in par- 

 ticular. I have already called your attention to the fact that that 

 proportion of coloured rays which, when combined, form white 

 sunlight, is that best suited to healthy life. It is necessary too to 

 that sufficient and proper stimulus to the organic changes which 

 go on in our bodies, and which we call a state of good health. 

 The various artificial lights differ very widely from sunlight in 

 this respect, that they are all more or less deficient in the rays 

 at the violet end of the spectrum, commonly called the actinic 

 rays, and which most probably exercise a very powerful effect 

 on the system. It is the want of a due portion of these violet 

 rays which makes all artificial light so yellow. Even the light 

 of the electric arc, which is richer in these rays than any other, 

 is still on the yellow side of sunlight. The incandescent electric 

 light is next best in this respect ; next in order come gas, petro- 

 leum, and the various oil lamps. No doubt some of you will 



1 Lecture delivered at the Health Exhibition by Mr. R. E. B. Crompton 



