5i8 



NATURE 



{April 2% 1878 



for this occasion or for any other purpose. If he has been 

 engaged in any scientific or literary research he should indicate 

 its character, and generally give evidence as to his previous 

 career and bond fides. The holders of the fellowships are 

 required to reside in Baltimore during the entire academic ses- 

 sion, and they are not permitted to engage in teaching, out of 

 the walls of the University, unless for exceptional reasons in 

 other colleges which may ask for some temporary service. They 

 are expected to devote all their time to study under the guidance 

 of one of the professors, or if there be no professor in the chosen 

 department, under the general approbation of the Faculty. 

 Toward the close of the Academic year a report of his work is 

 expected from each Fellow, As opportunities offer, the Fellows 

 are encouraged to prepare and read lectures or essays on subjects 

 to which they have given special attention. They are also 

 required to render occasional services as examiners or as 

 assistants in the laboratories ; but those services are not burden- 

 some, unless they are compensated by additional stipends. 

 Those who become distinguished by their attainments may be 

 assured of the constant encouragement of the Faculty. , With 

 all these precautions there seems little chance of the Johns 

 Hopkins University being eaten up by idle Fellows. 



SOCIETIES AND ACADEMIES 

 London 



Royal Society, April 11. — "The Acceleration of Oxidation 

 caused by the Least Refrangible End of the Spectrum," by 

 Capt. Abney, R.E., F.R.S. 



In a paper contributed to the Philosophical Magazine in 

 January last, the author expressed an opinion that Chastaing's idea 

 regarding an acceleration of oxidation being caused by red light 

 might prove true in regard to the oxidation of the photographic 

 image, and elsewhere ^ that Becquerel's coloured spectra might 

 be explained on the same principles, and this he finds to be true 

 as regards oxidation of the photographic image. 



A silver bromide film was exposed to diffused light. It was 

 then submitted to the action of the solar spectrum, whilst 

 immersed in a solution of potassium permanganate, hydroxyl, 

 potassium bichromate, or nitric acid, or in ozone. When the 

 strength of these was correct, a reversed image of the least 

 refrangible end of the spectrum was obtained, an increase in 

 oxidation taking place where the red rays acted, the reversal 

 commencing somewhere near D, and extending into the ultra -red. 



The accelerating effect of the red rays is most marked when 

 the solutions are weak ; but there is a limit to the dilution 

 caused by the fact that in the films employed the silver salt is 

 sensitive as far as the wave length 10,000, and there must be 

 sufficient strength to oxidise the invisible image as it is formed, 

 besides gi-adually destroying the effect of the preliminary 

 exposure. With silver iodide, as there is no reduction by the 

 red rays, the reversed action is much more readily obtained. 



A reversed image of the least refrangible end of the spectrum 

 can thus be produced by using solutions of a certain strength, 

 whilst if made more dilute an unreversed inmge is obtained. This 

 throws a light on Draper's photographs of this region of the 

 spectrum. 



Geological Society, March 6, — Henry Clifton Sorby, 

 F,R.S., president, in the chair. — Henry Edward Richard 

 Bright, George James Cotton Broom, William James Farrer, 

 George Scamell, and Joseph Fletcher White were elected 

 Fellows of the Society. — The following communications were 

 read : — On the geology of Gibraltar, by Prof, A, C, Ramsay, 

 F,R.S., and James Geikie, F.R,S. In this paper the authors, 

 after giving some account of the physical features of Gibraltar, 

 described in detail the various rock-masses of which the peninsula 

 is composed. The chief rock is a pale grey, bedded limestone, 

 overlain by shales containing beds and bands of grit, mudstone, 

 and limestone. Fossils are very rarely met with in the limestone, 

 and have never as yet been found in the shales. The only 

 recognisable fossil they obtained from the limestone was a 

 Rhynchonella, which Messrs, Etheridge and Davidson think is 

 most likely Rh. concinna. This would make the beds of Jurassic 

 age. The limestone forms the great eastern escarpment, and 

 dips west under the shales, which form the lower slopes upon 

 which the town is built. The dips vary from 12° or 20° up to 

 vertical. The connection of these strata with the rocks of the 

 adjoining districts in Spain and the opposite coast of Africa was 

 » "Treatise on Photography," p. 225. Longmans. 



traced, and it was shown that the Gibraltar limestone reappears 

 in Ape's Hill in Barbarj', while the overlying shales and the 

 sandstones of Queen of Spain's Chair form all the ground to the 

 west of Ape's Hill up to Cape Spartel, The Jurassic strata of Gib- 

 raltar are overlain by various superficial accumulations, the oldest 

 of which is a great mass of limestone agglomerate, which is 

 unfossiliferous, and shows as a rule no trace of stratification. It 

 is made up of angular blocks of limestone of all shapes and sizes, 

 and rests upon an uneven surface of limestone : it also covers 

 wide areas underneath which only shales are present. It is 

 excessively denuded, being worn into ravines and gullies, and 

 presents generally a^highly honeycombed surface. Terraces of 

 marine erosion have also been excavated in it. It is not now 

 accreting, and could not have been formed under present con- 

 ditions of climate and surface. The authors gave at length their 

 reasons for believing it to have been the result of a severe climate. 

 The blocks were wedged out by the action of frost, and the heaps 

 of angular debi-is thus formed were saturated by water derived 

 from melting snows, and so were caused to flow en masse down 

 the mountain slopes and over the gently inclined ground at their 

 base. The caves and fissures of Gibraltar were then described. 

 It was shown that the true bone-breccias were confined to these. 

 Many of these fossiliferous breccias are of later date than the 

 great agglomerate, since they are met with in fissures and caves 

 that intersect the limestone and limestone agglomerate alike. 

 When the mammalia tenanted Gibraltar, Africa and Europe were 

 united, and the climate was genial. All round the rock occur 

 platforms, ledges, and plateaus, which are evidently the work of 

 the sea. These erosion-terraces are covered in many places with 

 calcareous sandstones containing recent species of Mediterranean 

 shells. Such marine deposits occur up to a height of 700 feet. 

 The movement of depression was interrupted by pauses of longer 

 or shorter duration, and the climatic conditions were probably 

 much the same as at present. After the rock had been re- 

 elevated, the subaerial forces modified the surface of the marine 

 sands that covered the limestone platforms, so that they came to 

 form long sand slopes. The land at this period was of greater 

 extent than it is now, and some grounds exist for believing 

 Europe to have been again united to Africa, for mammalian re- 

 mains occur here and there in the deposits, that overlie the lime- 

 stone platforms. These relics, however, it is just possible may be 

 derivative. The climate was probably still genial like the present. 

 Overlying the marine and subaerial deposits just referred to occurs 

 an upper and younger accumulation of massive unfossiliferous lime- 

 stone agglomerate. This deposit the authors believe to owe its 

 origin to severe climatic conditions. After the marine deposits that 

 cloak so much of the eastern side of the rock had been weathered 

 into subaerial sand-slopes, large blocks were detached from the 

 cliffs and steep slopes, and these dropped down upon the sand 

 and were soon drifted over. By and by the blocks fell in such 

 quantities that the sand-slopes in many places were completely 

 buried under a talus of limestone dibris. This was subsequently 

 consolidated by infiltration into a solid agglomerate, in the same 

 way as the underlying sands were hardened into sandstone. 

 These sandstones contain a few blocks of limestone only in then- 

 upper portions. In their horizontally-bedded and lower-lying 

 portions no limestone blocks occur. This later agglomerate 

 bears every stamp of great antiquity, and could not have been 

 formed under present geographical and climatic conditions. The 

 surface is honeycombed and worn, just like that of the solid 

 limestone and the older limestone agglomerate. Since its accu- 

 mulation the climate has greatly changed, the present being 

 characterised by the absence of frost. In concluding, the authors 

 discussed at length the cause of the cold conditions that gave 

 rise to the great limestone agglomerates, and argued that this 

 cause could not have been elevation of the land. They also 

 pointed out that a submergence of the Sahara would be equally 

 incompetent to bring about the desiderated climatic conditions, 

 and that even a former much greater elevation of the land, com- 

 bined with the appearance of a Sahara sea, would fail to supply 

 us with the severe winter climate that was necessary to produce 

 the great agglomerates. They thought that the most probable 

 explanation of the phenomena described is that the cold con- 

 ditions referred to were contemporaneous with that general 

 refrigeration of climate which took place over so vast an area in 

 our hemisphere during pleistocene times. The limestone agglo- 

 merates they look upon as the equivalents of those glacial 

 deposits that occur so plentifully in our own and other countries, 

 and the bone breccias, which are intermediate in date between 

 the lower and upper limestone agglomerates, are paralleled by 

 the interglacial beds of the British Islands, Sweden, Switzerland, 



