luLV II, 1 901] 



ArA TURE 



259 



the present occasion the Director contents himself with 

 a very short preface, but which gives evidence of the 

 same untiring energy which marked the earher volumes. 

 For example, we are told that between 1S91 and 189S no 

 less than 473,216 photometric settings were made with the 

 meridian photometer, nearly all by the Director himself. 

 The object of this heavy undertaking was to determine 

 the magnitude of all stars brighter than 7-5 situated north 

 of -40' declination. In the early days of magmtude 

 work the Director did not propose to pass the limit of 

 - yy. This restriction was perhaps necessary on account 

 of the smaller photometer employed, but to overstep it 

 may also indicate that the Director feels himself now 

 competent to cope with the difficult questions arising 

 from the extinction of light in our atmosphere. For, 

 although the Durchmusterung does not aim at complete- 

 ness beyond - 40", a good many stars, reaching to even 

 within one degree oi the Harvard horizon, have been 

 included. Such measures are necessarily frequently dis- 

 cordant among themselves and do not agree with the 

 estimates made in the southern hemisphere, but the 

 discussion of all the discordant residuals, from whatever 

 source arising, is deferred till the appearance of another 

 volume. A difference of 0-65 mag. from the mean has 

 been selected as marking the limit of discordant 

 measures. 



It will be noticed that this photometric survey covers 

 no inconsiderable portion of the area that has been 

 examined by Kapteyn. The whole of the first volume of 

 the Cape Durchmusterung, - 18' to - 37'-, is included, 

 and should therefore furnish at once enlarged material 

 for the examination of the systematic differences between 

 photographic and visual magnitudes. Further, the meri- 

 dian Pickering photometer is at present at the Arequipa 

 Observatorv, having been dismounted in September iSgS, 

 and the energetic Prof. Bailey is presumably using the 

 same instrument at the southern station. Care has been 

 taken to interchange the observers at Harvard so as to 

 supply the means of reducing the observations on a uni- 

 form system, and thus continuing the Harvard survey to 

 the Southern Pole. We may therefore look forward to 

 the rapid acquisition of further data which will not only 

 afford better values for the constants of reduction of the 

 Cape plates, but exhibit in an unmistakable manner, 

 though it may not solve, the perplexing difficulties to 

 which we have alluded. Certainly, if energetic prosecu- 

 tion of the observations is of avail, the matter could not 

 be in better hands than those of the Directors of Harvard 

 and the Cape Observatories. \V. E. P. 



THE TREATMENT OF DISEASE BY LIGHT. 

 pHOTOTHER.-\PV,or the treatment of disease by fight, 

 ■*■ has now, thanks to Prof. Finsen of Copenhagen, a 

 recognised place in the domain of therapeutics. Finsen's 

 first paper on the subject was published in 1893. In it he 

 showed that the chemical or ultra-violet rays of .the spec- 

 trum have a definite effect upon the course of small-pox, 

 and he proposed that patients suffering from this disease 

 should be kept in rooms from which the chemical rays of 

 light were excluded by means of red curtains or red glass, 

 in the same way that a photographer excludes these rays 

 from his plates and paper. In an ordinary case of small- 

 po.x treated under the usual conditions, the eruption 

 passes from the vesicular to the suppurative or pus-form- 

 ing stage, and this condition is most marked upon the 

 face and hands, the parts most exposed to light. It is in 

 consequence of the destruction of the skin attendant upon 

 the suppuration that the face and hands are so commonly 

 the seat of hideous scars. Finsen's suggestion has been 

 carried out with considerable success. In nearly every 

 case in which the patient was kept in red light from the 

 onset of the disease, there has been found to be a marked 



NO. 1654, VOL. 64] 



change in the course of the eruption. The suppuration 

 and its attendant secondary fever have been almost, if not 

 entirely, abolished, and as a result the patients recover 

 with little, if any, scarring. 



Finsen's next researches were made upon the action of 

 light as an irritant, and they are of extreme interest to 

 the biologist. It will suffice here to say that he found 

 that the animal organism, especially in creatures which 

 prefer to dwell in the dark, is markedly irritated by the 

 chemical rays, while the other parts of the spectrum 

 are non-irritant. From this he was led to investigate 

 the effects of light upon bacteria. Here the field had 

 already been occupied by Downes and Blunt, who, in 

 1S78, in a paper read before the Royal Society, showed 

 that the chemical rays are bactericidal. Duclaux, Arloing 

 and others have worked upon the same lines and confirmed 

 their results. It therefore seemed probable that super- 

 ficial diseases of the skin caused by bacteria could be 

 cured by the application of light. Of these, one of the 

 most important and most intractable is lupus. Finsen, 

 however, argued that the intensity of ordinary sunlight is 

 obviously insufficient to kill the microbes as they lie in 

 the skin, for lupus is particularly a disease of the face, 

 which is more exposed to the sun than any other part. 

 He therefore tried the effect of concentrating the light 

 by means of lenses, cutting out the red and ultra-red rays 

 by a blue medium. He found that cultures of micro- 

 organisms in vitro were much more powerfully influenced 

 by the concentrated rays. The suns rays concentrated 

 by the apparatus to be presently described were fifteen- 

 times stronger than ordinary sunlight. Powerful electric 

 arc lights were also tried, and with a lamp of from 35 to 

 jo amperes the effect was similar to that of the sun, or 

 even greater. 



The next point to be determined was the penetrative 

 power of light. For this purpose small sealed tubes con- 

 taining silver salts were placed under the skin of animals- 

 and exposed to the concentrated light, and the silver was 

 found to be blackened. 



The effect of the blood circulating in the tissues was 

 next demonstrated by a very ingenious experiment. A 

 piece of photographic paper was placed behind the ear, 

 and the outside of the lobule was exposed to the light. 

 In about five minutes the paper was blackened. The 

 experiment was then tried with the ear compressed be- 

 tween two pieces of glass so that it was rendered blood- 

 less. The photographic paper was blackened by the 

 light in twenty seconds. The absence of the red colouring 

 matter of the blood allowed the chemical rays to penetrate 

 with great ease. 



The apparatus devised by Finsen for the treatment of 

 lupus by the sun's rays (Fig. i) consists of a large hollow 

 planoconvex lens, filled with an ammoniacal solution of 

 sulphate of copper and mounted upon a fork-like metal 

 stand, so arranged that the lens can be moved about a 

 horizontal and also round a vertical axis, and lowerer* 

 and raised at will. The filtered sun's rays are focussed 

 upon the area of skin to be treated, and at this spot is- 

 placed the compression apparatus. This is a very flat 

 cylinder made of two plates of rock crystal fixed in a 

 nietal ring. Through the compression apparatus passes 

 a current of cold water, so that the instrument is used 

 to render the part to be treated bloodless and also t& 

 cool it. The pressure apparatus is held on the skin by 

 a nurse throughout the whole sitting, which lasts one hour 

 or a little more. The spot treated at each sitting is about 

 the size of a sixpence. 



The electric light apparatus (Fig. 2) is much larger and 

 more complicated. Attached to a strongmetal ring round a 

 large arc lamp, of 30,000 to 35,000 candle-power, are four 

 long cylinders like telescopes. Each telescope consists 

 of two parts. The upper part, closed at each end by 

 rock crystal lenses, makes the divergent rays of the arc 

 light parallel, and the lower piece brings the rays thus 



