May 10, 1883] 



NA TURE 



45 



no portion of the conductor should ever .be allowed to attain a 

 temperature exceeding 150 F. 



8. Under ordinary circumstance-; cor.plete metallic circuits 

 should he used ; the employment of gas or water pipes as con- 

 ductors for the purpose of completing the circuit should not in 

 any case be allowed. 



9. Bare wires passing over the tops of houses should never be 

 less than seven feet clear of any part of the roof, and all wires 

 crossing thoroughfares should invariably be high enough to allow 

 fire-escapes to pass under them. 



10. It is most essential that joints should be electrically and 

 mechanically perfect and united by solder. 



11. The position of wires when underground should be clearly 

 indicated, and they should be laid down so as to be easily in- 

 spected and repaired. 



12. All wires used for indoor purposes should be efficiently 

 insulated, either by being covered throughout with some insu- 

 lating medium, or, if bare, by resting on insulated supports. 



13. When these wires pass through roofs, floors, walls, or parti- 

 tions, or where they cross or are liable to touch metallic masses, like 

 iron girders or pipes, they should be thoroughly protected by 

 suitable additional covering ; and where they are liable to 

 abrasion from any cause, or to the depredations of rats or mice, 

 they should be efficiently incased in some hard material. 



14. Where indoor wires are put out of sight, as beneath 

 flooring, they should be thoroughly protected from mechanical 

 injury, and their position should be indicated. 



N. B. — The value of frequently testing the apparatus and 

 circuits cannot be too strongly urged. The escape of electricity 

 cannot be detected by the sense of smell, as can gas, but it can 

 be detected by apparatus far more certain and delicate. Leakage 

 not only means waste, but in the presence of moisture it means 

 destruction of the conductor and its insulating covering, by 

 electric action. 



III. Lamps 



15. Arc lamps should always be guarded 'by proper lanterns 

 to prevent danger from falling incandescent pieces of carbon, 

 and from ascending sparks. Their globes should be protected 

 with wire netting. 



16. The lanterns, 'and all parts which are to be handled, 

 should be insulated from the circuit. 



IV. Danger to Person 



17. Where bare wire out of doors rests on insulating supports, 

 it should be coated with insulating material, such as india- 

 rubber tape or tube, for at least two feet on each side of the 

 support. 



18. To secure persons from danger inside buildings, it is 

 essential so to arrange and protect the conductors and fittings 

 that no one can be exposed to the shocks of alternating currents 

 of a mean electromotive force exceeding 100 volts, or to con- 

 tinuous currents of 200 volts. 



19. If the difference of potential within any house exceeds 

 200 volts, the house should be provided with a "switch," so 

 arranged that the supply of electricity can be at once cut off. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE 



Cambridge. — Dr. Humphry has formally resigned the Pro- 

 fessorship of Anatomy, after having taught anatomy in the 

 University for thirty-six years, at first as assistant to Prof. Clark, 

 and since 1866 as Professor. The Electoral Board for the Pro- 

 fessorship consists of Professors Huxley, Allen, Thompson, 

 Flower, Paget, Newton, and Liveing, Dr. Michael Foster, and 

 Mr. J. W. Clark. 



The Honorary Degree of LL.D. will be conferred in June 

 upon Count Menabrea, formerly Italian Ambassador to England, 

 Prof. Pasteur, Prof. Michaelis (Strasburg), Sir A. Grant, Bart., 

 Principal of Edinburgh University, Sir John Lubbock, Bart., 

 Sir J. A. G. Ouseley, Bart., Professor of Music at Oxford, Sir 

 Richard Temple, Bart., Lieut. -Gen. Walker, Surveyor-General 

 of India, Mr. Matthew Arnold, Prof. YV. W. Goodwin (Har- 

 vard, U.S.), Mr. Reginald S. Poole (British Museum), Prof. 

 H. E. Roscoe (Owens College), and Mr. G. F. Watts, R.A. 



The Graces creating a Professorship of Surgery without sti- 

 pend, and authorising the immediate appointment of a Professor 

 of Physiology, are to be voted on to-day (Thursday). 



The City and Guilds of London Institute has decided to 



make a grant of 300/. a year for five years, for the purpose of 



supporting a Chair of Mechanical Engineering in connection 

 with Firth College, Sheffield. 



SOCIETIES AND ACADEMIES 

 London 

 Royal Society, March 15. — "Atmospheric Absorption 

 in the Infra-Re 1 of the Solar Spectrum." By Capt. Abney, 

 R.E., F.R.S., and Lieut. -Col. Festing, R.E. 



Any investigations on the subject of atmospheric absorption 

 are of such importance in the study of meteorology, that we 

 have deemed it advisable to present a preliminary notice of cer- 

 tain results obtained by us, without waiting to present a more 

 detailed account which will be communicated at a future date. 

 From 1874, when one of us commenced photographing the 

 spectrum in the above region, till more than a year ago, the 

 extremely various manners in which the absorption took place 

 caused considerable perplexity as to their origin, and it was only 

 after we had completed our paper on the absorption of certain 

 liquids ' that a clue to the phenomena was apparently found. 

 Since that time we have carefully watched the spectrum in rela- 

 tion to atmospheric moisture, and we think that more than a 

 year's observations in London, when taken in connection with a 

 month's work at an altitude of 8500 feet on the Riffel, justify 

 the conclusions we now lay before the Society. 



A study of the map of the infra-red region of the solar spec- 

 trum, 2 and more especially a new and much more complete one, 

 which is being prepared for presentation to the Royal Society 

 by one of us, shows that the spectrum in this part is traversed 

 by absorption lines of various intensities. Besides these linear 

 absorptions, photographs taken on days of different atmospheric 

 condition show banded absorptions superposed over them. These 

 latter are step by step absorptions increasing in intensity as they 

 approach the limit of the spectrum at the least refrangible end. 

 In the annexed diagram 3 Fig. 4 shows the general appearance 

 of this region up to A 10,000 on a fairly dry day : the banded 

 absorption is small, taking place principally between A 9420 and 

 A 9800 : a trace of absorption is also visible between A 8330 

 and A 9420. On a cold day, with a north-easterly wind blowing, 

 and also at a high altitude on a dry day, these absorptions nearly 

 if not quite disappear. If we examine photographs taken when 

 the air is nearly saturated with moisture (in some form or 

 another) we have a spectrum like Fig. 1. Except with very 

 prolonged exposure no trace of a spectrum below A 8330 can 

 be photographed. Fig. 2 shows the absorption-bands, where 

 there is a difference of about 3° between the wet and dry 

 bulbs, the latter standing at about 50°. It will be noticed 

 that the spectrum extends to the limit of about A 9420, 

 when total absorption steps in and blocks out the rest 

 of the spectrum. Fig. 3 shows the spectrum where the 

 difference between the wet and the dry bulbs is about 6°. 

 Figs. 5 and 6 show the absorption of thicknesses of I foot and 

 3 inches of water respectively, where the source of light gives a 

 ! continuous spectrum. With J-inch of water all absorption- 

 | bands except that commencing at A 9420 are absent. It will be 

 I seen that there is an accurate coincidence between these " water- 

 bands " and the absorption-bands seen in the solar spectrum, 

 and hence we cannot but assume that there is a connection one 

 with the other. In fact, on a dry day it is only necessary to 

 place varying thicknesses of water before the slit of the spectro- 

 scope and to photograph the solar spectrum through them, in 

 order to reproduce the phenomena observed on days in which 

 there is more or less moisture present in the atmosphere. It is 

 quite easy to deduce the moisture present in atmosphere at cer- 

 tain temperatures by a study of the photographs. There does 

 appear a difference, however, in the intensity of the banded 

 absorptions in hot weather and in cold about up to 50'. In the 

 former they are less marked when the degree of saturation 

 and the length of atmosphere traversed are the same as in the 

 latter. 



The accepted view, we believe, of absorption of vapours is 

 that they give linear absorptions in [certain thicknesses, and as 

 the thickness increases or the density becomes greater, the lines 



1 "The Influence of the Atomic Groupings of the Molecules of Organic 

 Bodies on their Absorption in the Infra-Red Region of the Spectrum." 

 Phil. Trans., Part III., 1881. 



= Phil. Trans., 1880. 



3 The black lines given in the diagram are merely lines of reference, and 

 do not represent the aqueous absorption under consideration. 



