November, 1906.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



583 



to five degrees, particularly in Japan. Seismic centres 

 abound especially where there are such contrasts as a 

 steep submarine strata, terminating in a very abrupt 

 terrestrial slope. There are constant disturbances 

 along the crevasses. There is a shrinkage of the crust 

 along the dislocations, and they provide, as it were, 

 a safety valve for internal disturbances. In other 

 words, the volcano and the earthquake are brothers and 

 not father and son, as it has been thought for a long 

 time in default of sufficient observation. 



The secular cooling has induced folds and hollows 

 of solidified external crust on the pulpy shell, which 

 goes on contracting, so that the.se noises are not only 

 rumblings, but they are accompanied by movements; 

 for the enormous pressure from the interior induces up- 

 heavals and volcanos. Heat, hot water, and steam, are 

 all at work; ruptures of equilibrium are accompanied by 

 puffs of elastic gas, showing the existence under our 

 feet of a considerable tension, which is always ready 

 for action. 



Chains of mountains and maritime slopes result from 

 the gradual cooling of the globe, the cracking of the 

 crust, which, being forced tO' a base, descend more or 

 less. These cracks cannot occur without some di.s- 

 turbanoss; and, as I said before, they occur constantly 

 every day and every hour. We only notice the most 

 violent ones, which bring disaster to us. But, as a 

 matter of fact, earthquakes are regular and normal 

 episodes in the life of our planet. 



The new science of seismology has been created by 

 statistics, agglomeration and classification of the docu- 

 ments. Alexis Peirey, a learned compatriot and col- 

 league of the Academy of Dijon, made a catalogue of 

 the thousands and thousands of shocks mentioned every- 

 where from 1844 to 1872. I tried to continue this 

 catalogue in my review. Astronomy, from 1883 to 1888, 

 with the help of my laborious colleague, C. Detaille. 

 Hut these statistics took up so much room that we had to 

 give them up. It has been continued for several vears, 

 with scrupulous and indefatigable care, by M. de 

 Montessus, of Ballore, in the excellent Belgian review, 

 del et Tcrrc. This mass of documents records more 

 than 170,000 earthquakes, which give room for the 

 study of .seismological geography. According to the 

 general synthesis of M. de Montessus, of Ballore, which 

 embraces the whole world, it is seen that the terres- 

 trial crust trembles nearly equallv, and almost solelv 

 along the two narrow zones which cross at an angle 

 of 67 degrees, the Mediterranean or .Alpine Caucasian 

 and the circimi-Pacific circles. These two zones coin- 

 cide with the two most important lines of the terrestrial 

 surface. Earthquakes are common on the most mobile 

 strips of the terrestrial surface, where great accumula- 

 tions made have been dislocated and r:iiscd in the 

 tertiary perio'd, before the formation of the princip.il 

 actual chains. 



Birkbeck College.— The Rt. Hon. R. B. Haldane, M.P., 

 distributed the prizes at the Birkbeck College, on Friday, 

 October 26, and lectures have been delivered during the past 

 month by Professor Plinders Petrie, Mr. .S. L. Bcnsusan, 

 and Professor II. Von Herkonier, R.A. Among the other 

 lecturers of the present term are Mr. llilairc Belloc, M.P., 

 Dr. James Cantlie, .Mr. E. Thompson Seton ; and next term 

 lectures by Mr. E. T. Reed, of Punch, Miss Gertrude Bacon, 

 and Dr. J. D. McClurc, K.R.A.S., are promised. The 

 summary of examination results shows that in the past vear 

 fourteen Birkbeck College students passed the Loiidon 

 B..Sc. (six with honours), and live the B..\. Hnal ; twenty- 

 eiyht the Intermediate Science, and seven the Intermediate 

 Arts. 



Photography. 



Pure and Applied. 



By Chapman Jones, F.I.C., F.C.S., &c. 



Fhologi-aphy of the Infra-Tied. — M. G. Millochau 

 describes in the Comptcs Rcndtis (1906, cxlii. 1407, and 

 cxiiii., 108), the method he is employing for photo- 

 graphing the infra-red and mapping this part of the 

 solar spectrum. He follows on the lines adopted by 

 M. Stefanik, who, by the use of coloured screens to 

 absorb the more easily visible parts of the spectrum, 

 finds that he can get the extreme violet (H and K) to 

 appear very brilliant, and can easily see to about X3830 

 (L), which is as far as some glass instruments trans- 

 mit, and can similarly extend the visibility of the 

 spectrum in the infra-red. M. Millochau uses a deeply- 

 coloured alcoholic solution of chrvsoidine, malachite 

 green, and aniline violet to cut off the light other than 

 the extreme and infra-red. Tlie plates u.sed are first 

 exposed to diffused light to fog them, advantage being 

 taken of the fact that the light at the red end of the 

 spectrum reverses or negatives the ordinary exposure 

 effect. But as the reversing action has been found to 

 be little more that superficial, it is advantageous to 

 stain the film and so prevent the preliminary exposure 

 effect from penetrating so^ deeply as it otherwise would. 

 The preparation of the plates in actual practice is as 

 follows : — Lumiere's 2 plates are soaked in water for 

 fifteen minutes, then soaked in a well-filtered, saturated 

 alcoholic solution of either chrysoidine, or erythrosine, 

 or (less advantageously) eosine, rapidly rinsed, and 

 dried. The preliminary exposure follows, artificial 

 light being used, but further details of it are not given. 

 By this means M. Millochau has mapped the solar 

 spectrum from '^8377 to '^9325. 



Reversal by Red Light. — It is interesting to note that 

 the reversing action of the extreme red and infra-red 

 rays, as mentioned in the previous paragraph, is almost 

 sui>erficial, as this is evidence in favour of the sup- 

 position that the air has something to do with the 

 reversal, and that perhaps it is due to oxidation, a 

 theory that has been suggested bv several observers, 

 especially .\bney. But all exposure effects begin at the 

 surface that the light impinges upon, and one would 

 like some proof, in this particular case, that the infra- 

 red light really has had time to work through or well 

 into the gelatine film, so that the superficial character 

 of the reversal is not due merely to a want of pene- 

 trating power of the light. In this connection may be 

 noted the recent observation of Messrs. Precht and 

 Stenger, that rc\ersal by over-exposure is retarded by 

 treating the plate with a i per cent, solution of a de- 

 veloping agent before exposure, a plate so treated re- 

 quiring more than forty times thecxp>osure it previously 

 needed to produce reversal; as well as the much older 

 experiments of Abney, in the similar use of reducing 

 agents, and the exclusion of air. But in forming a 

 theory as to the action of light in producing reversal 

 effects, it is not sufficient, as one is so often tempted 

 to do, to consider experiments of one kind only, how- 



