KNOWLEDGE .S: SCIEXTIEIC NEWS. 



[October, 1905. 



That is, the amount of obliquity causes the sun to be slow, or it 

 has no effect. Can anyone explain away these two days if they 

 exist or show that any cause is operating to reduce them ? I 

 would like to touch upon'otherpoints, but fear I have exceeded 

 allowable limits. 

 August 17, 1905. A. Balding. 



By the courtesy of the Editor I have seen Mr. Balding's 

 letter, and I at once admit that my supposed challenge was a 

 little hasty, since an obliquity of no' is a sort of paradox, and 

 its effect would be less obvious than that of an obliquity of 

 marly 90'. .Apparently, however. Mr. Balding fully realises 

 the sort of effect to be expected. The appeal to Ck-sar may 

 stand, and we may admit the approximate accuracy of the 2-. 

 But two degrees will not mean two days, as >tr. Balding 

 imagines, since, as he himself allows, the motion is not that of 

 the sun but of the earth, so 2'- means about S minutes of time, 

 or 16 seconds (roughly) per day. A very different matter to 

 his I hour 36 minutes. — The Reviewer.] 



Eoliths- 



TO THE EDITORS OF " KNOWLEDGE & ILLISTRATED 

 SCIENTIFIC NEWS." 



Sirs, — A recent experiment in France is reported whereby 

 so-called Eoliths were produced by mechanical means ; the 

 impression caused by the report is likely to lead to some dis- 

 cussion on the nature of Eoliths. It appears that certain 

 French authorities visited a cement factory at Mantes for the 

 purpose of examining certain stones chipped during some 

 mechanical process whereby flints are separated from the 

 chalk matrix. At the conclusion of the process they were 

 astonished to find '• that the great majority presented examples 

 of all the Eolithic forms." On this point of similarity it is 

 necessary to suspend opinion, but the observers have, as a 

 result, abandoned all conviction that Eoliths had an .artificial 

 origin. No one doubts that stones somewhat resembling 

 Eoliths can be produced by natural processes — the Mantes 

 process it should be borne in mind is not a natural one— but 

 at the same time there is a distinction to be drawn between 

 them and true Eoliths. Again, with all respect to Continental 

 observers, it may be said that much of what is there accepted 

 as of human origin would here be rejected as too indefinite. 

 In what w;iy it can be shown that the Mantes mechanical 

 process resembles the action of the rivers in depositing the 

 plateau or any other gravels is difficult to understand. We 

 are told that the flints and the containing chalk blocks are 

 placed in a receiver full of water, and then rotated to effect 

 separation; but here is no parallel ot action, as in the 

 separating process the materials are strictly confined within 

 the receiver. We are further informed that the majority of 

 flints thus separated show work of seeming Eolithic type. In 

 this feature the plateau gravel compares unfavourably with 

 the Mantes process, for in the former the worked stones form 

 but a small proportion of the whole. It should be remarked 

 that unrolled Eoliths often occur with rolled flints, and that the 

 clayey nature of some plateau gravels preclude the- necessity 

 of supposing a violent type of deposition ; in fact, the presence 

 of this clay serves to show that in some cases deposition went 

 on in a tranquil manner, or under circumstances not favourable 

 to the abrasion of flints. How, it may be asked, can the 

 presence of unrolUd Eoliths in this clayey drift be explained 

 away other than by suggesting that they were dropped near 

 these ancient streams and subsequently covered by the con- 

 taining clay ? 



I'nder any circumstances the Mantes pseudo- Eoliths do not 

 dispose of the evolutionary contention for a period when man 

 had not arrived at the Palitolithic stage of his culture. 

 Professor Boule and Dr. Obermaier will shortly discuss these 

 psendo- Eoliths, when they will doubtless give reasons for the 

 contention that a modern mechanical process can be admitted 

 as evidence against fh<> h-imnn origin of Eoliths. 



That natural a-; ' ure flints is admitted, but the 



n.-iture of the tract said to bear with it its own 



explanation; anot:. ,n is demanded by the definite 



types of Eolithic iriit.;. :i:miI,. For this re.-ison, then, all 

 students of these early forms will await with interest the 

 advent of these pseudo Eoliths from the Mantes cement yards 



Chelsfield, Kent, Yours faithfully, 



August 17, 1905. J. KISSELL Lahkhv. 



Photography. 



Pure and Applied. 



By CH.iP.MAN Jones, F.I.C, F.C.S., &c. 



Scnsiiiicrs. — The action of certain dyes and .•similar 

 organic substances as sensitisers for photofjraphic 

 plates, ospcciaJly for conferring' increased sensitiveness 

 to green and red light, is so well known that it is 

 interesting to note the effect of similar bodies wheji 

 added to other light-sensitive substances. Messrs. M. 

 Calmels and L. P. Clerc (I.e Men. de la Phot., July ; 

 .Abstract, Jul. Royal Phot. Sac, .August) have experi- 

 mented in this direction with bichromated gelatine and 

 albumen, as used in photo-mechanical work (making 

 process blocks). One sample of erythrosin doubled the 

 sensitiveness of a gelatine film, another increased it to 

 three times, while a sample of eosin made it four times 

 as sensitive as when untreated. From two to four 

 grams of the colouring matter to cacli litre of the pre- 

 pared bichromaled solution of gehitinc or alluiiiKn is 

 about the maximum c|uantity, and when more than this 

 is added the scnsitivenc.ss of the resulting film is de- 

 creased. Messrs. A. Jodlbauer and H. V. Tappciner 

 {Ber. p. 2602 ; .Abstrr-ct, Jul. Sac. Client. Iiid., p. 903) 

 find that the sensitiveness to light of a solution of 

 mercuric chloride and ammonium oxalate (;ui used in 

 photometry) is increased by the addition to it of cer- 

 tain fluorescent substances, including fluorescein and 

 its chlorine, bromine, and iodine derivatives. It would 

 be interesting to know the character of the added sen- 

 sitiveness in these cases, whether the substances used 

 are "colour sensitisers," as the expression is used in 

 relation to gelatine and colltxlion plates. But, in any 

 case, until it is shown to be otherwise, a broad dis- 

 tinction must be made between the effects just referred 

 to and the sensitising of silver s;dts, because, in tlic one 

 case, it is a definite chemical change that is quickenod, 

 while in the other the change is presumably not chemi- 

 cal at all, though, further than tJiis, nothing is known 

 of its real nature. 



llie Principles of l)evclo[>mc>it, etc. — 'Hie recent com- 

 munications of Messrs. Sheppard and Mees deal with 

 matters that have an important be:iring upon photo- 

 graphic procedure, and from them I have gathered the 

 following results and conclusions. It must not be sup- 

 posed that these results can be applied without modi- 

 fication to all circumstances that appear to be similai 

 to those staled, as investigators c.innot be held re- 

 sponsible for the moclifications that plate-makers maj 

 see fit to introduce into their forniulie, or photographers 

 into their methods. The plates used were, I believe, 

 .•-peciailv prepared by coating iil.ile gl.iss with a simple 

 emulsion containing less than one per cent, of silver 

 iodide, and the minimum of soluble salts. 



The quantity of silver that is found in 100 square 

 centimetres of film after exposure and develo[)ment to 

 give a "density" (opacity logarithm) of unity, the 

 authors find to be .01031 gram as a mean of several 

 experiments. luler had previously obtained the same 

 figure, but Hurler and Driffield found .0121, and sub- 

 se(|uently, .0131 gram. 'Ihe authors suggest that this 

 discrepancy is due either to a constant error in llurtcr 

 and IJrilHeld's photometer, or else to the plates used. 

 I believe th-it it is a common experience with plate- 

 makers that very much more silver is necessary to 

 giw* density in a quick plate than in a slow one From 

 this, and other considerations, I should have expected 



