62 



NATURE 



\May 23, 1872 



Puys, and on the border of a lake which was actually 

 formed by the damming up of a stream by one of the most 

 recent of the la\a-currents) to Mamertus, Bishop of Vienue, 

 in which he speaks of the earthquakes that had occurred 

 in the neighbourhood of Vienne ; of fire issuing from the 

 earth and wild beasts taking refuce in cities ; and the 

 Rogation Homily of Alcimus Avitus, the successor to 

 Miunertus, which mentions the same catastrophes. 



Now in the first place Vienne is more than seventy 

 miles in a direct line from the more recent Auvergne vol- 

 canoes ; in the next, Sidonius himself makes no menlion 

 in his writings of any eruptions having taken place in his 

 neighbourhood, although he wrote poems describing the 

 beauty of the scenery : and lastly Auvergne is not 

 mentioned by any ancient writer, neither by Cassar, who 

 encamped there and laid siege to Gergovia.a city situated 

 on atable-land,with craters close at hand in almost every 

 direction ; nor by Pliny, who gives a list of all the then 

 known volcanic countries, including some very out-of-the- 

 way ones ; nor by Strabo, nor by any of the poets, as a 

 country where volcanoes were ever known to have been in 

 action. 



For these reasons, and because no volcano could have 

 burst out near Vienne without leaving some traces of its 

 existence. Dr. Daubcny concluded that the bishops of 

 Gaul alluded to earthquakes ; especially as " the under- 

 ground thunder, the opening of fissures in the ground, 

 the bursting out of flames and gases, the projection of 

 water and of stones, the smell of sulphur, the alarm 

 evinced by the animals of the spot and neighbourhood, 

 the elevation or depression ol the land, noticed by 

 Sidonius and by Avitus in the passages referred to by Sir 

 Francis Palgrave, are all reported as concomitants of the 

 great earthquakes which have occurred in more recent 

 times." Geologists have since accepted this conclusion 

 as the correct one , in opposition to what I may call the 

 theological position. 



There was, however, a volcanic region which had not been 

 visited by any English geologist, and which had not been 

 described, viz., the basin of Montbrison, through which the 

 Loire flows. Of this Mr. Scrope says in his work (2nd 

 Ed., p. 28), '' a further examination of this basin seems 

 very desirable ; " now as this district lies about half way 

 in a direct line between the " Puys," about Clermont Fer- 

 rand and Vienne, it occurred to Dr. Daiibeny that the 

 disturbances spoken of as in the neighbourhood of Vienne, 

 might have taken place around Montbrison, and accord- 

 ingly in the autumn of 1S66 he visited that locality, and 

 1 had the honour of accompanying him on the occa^ion. 

 We examined carefully the volcanic hills of the neigh- 

 bourhood, and could find no trace of recent volcanic erup- 

 tions ; in his own description of this expedition published 

 in the (2iiiii'/t-r!y Journal ofScit-nce for January 1867, and 

 republished in his " Miiceilanies " (vol. i. p. 74), just be- 

 fore his death, he says : — 



'• 1 am now prepared to say that, without pretending to 

 have surveyed the entire district, I saw enough to con- 

 vince me that no volcanic disturbance which had occurred 

 within this area at so late a period as that aduded to 

 could have escaped our notice, and that every indication of 

 i<Tneous action which presents itself throughout the 

 countr.', bears marks of a much greater antiquity. 



"Thus much, at least, I can venture to affirm, namely, 

 that neither, craters, streams of lava, scorias, nor even 

 cellular trap, are to be met with anywhere within the 

 limits of this district. On the contrary, the only igneous 

 rocks which came under our observation consisted of a 

 compact basalt, containing nests of olivine, a material 

 which could only have been elaborated by the aid of great 

 pressure, and under a different contiguration of the surface 

 from that now existing." 



The Doctor therefore reiterated his statement that ''the 

 lively picture drawn by Sidonius " should not " be re- 

 garded in any other light than as the offspring of a lively 



imagination, dwelling upon reports which had reached the 

 author with respect to some fearful earthquake which 

 may have occurred in the neighbourhood of Vienne."* 



1 will conclude by advising those who wish to study 

 volcanic phenomena to go to Auvergne, they can do so at 

 almost any time of the year, mid-winter, when it is far too 

 cold (or comfort, being the exception ; they will there see 

 results of volcanic action far more varied and instructive 

 than at Vesuvius or even at Etna, and they will also be 

 able to study the effects of denudation on a gigantic scale. 

 Few geologists seem to appreciate the fact that within 24 

 hours of London is one of the largest, richest, and most 

 beautiful of the volcanic countries in Europe. 



W. H. CORinELD 



PHOTOGRAPHY AS AN AID TO SCIENCE 



THE applications made of photography now-a-days are 

 as various as they are numerous. Irrespective of 

 the ordinary every-day uses to which the art is put in 

 reproducing scenes and objects, or pandering to human 

 vanity, there are, as we know, numberless ways in which 

 it is constantly being employed as a faithful handmaiden 

 to science. To the chemist, the surgeon, the engineer, 

 and others, its aid is frequently of considerable impor- 

 tance, while to the astronomer and physicist the assistance 

 it renders is at times indispensable. The accuracy and 

 fidelity with which the pencil of light performs its func- 

 tions, combined with the facility with which such reliable 

 records are obtained, make photography indeed one of the 

 greatest boons at the disposal of scientific men. 



Let us take, for example, the solar records which are 

 daily secured at the Kew Observatory. These photographs 

 of tiie sun's disc, taken whenever practicable at a certain 

 fixed period in the day, are often of considerable value, 

 and form illustrations, as it were, of other scientific obser- 

 vations made at the same time. A series of prints of this 

 kind, secured day after day, afford, in trutli, a most in- 

 teresting and instructive lesson to the student of astronomy, 

 for the characteristics exhibited by the various photographs 

 may serve as a corroboration, or otherwise, of scientific 

 theories based upon other data and results. The nature 

 and luminosity of the markings, or spots, upon the disc 

 are rendered with unerring fidelity, and the way in which 

 these are continually modified in shape and intensity, as 

 likewise the rapidity with which they are seen to travel 

 across from the eist to west limb of the sun, to reappear 

 again some twelve days afterwards upon the eastern edge, 

 is all clearly and distinctly shosvn. 



Again, another interesting application of photography 

 to astronomic purposes is to be found in the reproduction 

 of the stars as recently undertaken by Prof. Ruther- 

 ford, ^n this instance the objects to be secured are so 

 minute that special precautions are necessary in depicting 

 them upon the sensitive film, so that their impressions 

 may be distinguibhable from accidental specks in the col- 

 led on plate. To prevent any such chance of mistake, 

 Prof Rutherford secures a double ima;;c of each luminary, 

 the moving telescope to which the miniature camera is 

 attached being halted for a short time (half a minute) 

 between a first and second exposure of the plate, so that 

 each star is represented by a double speck, so to speak, 

 upon the negative, and is clearly to be distinguished 

 therefore, from any accidental defect in the film ; more- 

 over, by stopping the telescope again after the period 

 necessary for the second exposure, the professor is 

 enabled to demonstrate the direction in which the stars 

 are moving, for the brightest of them produce a tiny 

 streak of light during the time that the camera remains 

 perfectly still. A map or plan of the heavens is in this 



* Those who wLsh for fiirtlier information will find the whole subject dis- 

 cussed in Dr. Daubcny 's classical work on Volcanoes, and in his papers in the 

 Quarterly younwl 0/ Science for April 1866 and January 1867. 



