174 



KNOWLEDGE & SCIENTIFIC NEWS. 



[August, 1904. 



to saying- that at some early period ai breed of long-- 

 niancd horses was introdi:ced from the cast into Europe, 

 wiiich resukod in soi nvwiifyinK the original hc>ij--!nancd 

 stock as to render floavin^^ manes universal; and if this 

 be the case, we have to attribute a mixed, vr dual, 

 orit^in to the ordinary, or so-called " cold-blooded "' 

 horses. Traces of the indigenous ijlood may, perhaps, 

 be detected in the apparently stouter build of the horses 

 of the Greek sculptures as compared with those oi the 

 l^t;;-yptiaa frescoes and Assyrian bas-reliefs. 



In comparatively modern times another importation 

 of eastern blood is definitely known to have taken place, 

 which, by careful restriction, has resulted in the pro- 

 duction of the existinij thnrouylibred. The Arabs and 

 Harbs from which this thoroug-hbred strain origfinated 

 were themselves, in all probability, the direct unmixed 

 product of the aforesaid long--ma,ned horses of ancient 

 Assyria, Babylonia, and Ef^ypt, which we have seen 

 reason to. believe arose from a totally different stock to 

 the hog-maned breed of Europe. 



With reg-ard toi the ultimate ancestor of the thorough- 

 bred and its early Asiatic prot^enitor, opinions differ. 

 IVofessor Ridgeway,* of Cambridge, has reccntl\- 

 'Suggested that Grevy's zebra {Equiis girvyi), of Somali- 

 land and North-East Africa, is the prohable ancestor of 

 the thoroughbred stock. Such a solution of the ques- 

 tion, will not, however, I venture to. think, commend 

 ilself for a moment toi competent zoolog-ists, and I need 

 not," therefore, attempt its refutation,. 



From the occurrence in a horse-skull of eastern origin 

 in the British Museum of a remnant O'f the cavity for 

 the face-gland of the Hipparions, and of a fainter trace 

 of the same in the skull of the thoroughbred " Bend Or," 

 I have been led to suggest that the thoroughbred and 

 eastern breeds generally may be derived fro'm an 

 extinct Indian, species — 'Eiiuhs. sivahnsis — in which this 

 face-gland was comparatively well developed; and that, 

 as might have been expected, easterui horses retain 

 traces of the face-gland cavity, which, as we have seen, 

 has been completely lost by the prehistoric horses of 

 Western Europe, as it is by their presumed cross-bred 

 existing descendants. It must be confessed that the 

 evidence in favour of this theory is at present slender; 

 and the examination: of a series of skulls of Arabs and 

 thoroughbreds is necessary to test its probability. As 

 it is, all that can be said in its favour is that it affords a 

 working hvpothesis which accords well with the facts. 



In conclusion, I may mention that a correspondent 

 has informed me that a few years agO' be owned a horse 

 which showed distinct external traces of the face-gland, 

 in the form of a well-marked depression in front of each 

 eye. The horse referred toi was believed to have been an 

 Argentine, and if this be true, another very curious 

 point arises. Certain extinct South American horses, 

 constituting the genus Onohippidium, are characterised 

 by the enormous size of the cavity for the face-gland, 

 which was no. doubt functional. From the condition of 

 their remains they certainly lived till a comparatively 

 recent date; and it is possible they may have survived 

 till the Spanish exploration of South .America, for if the 

 horses seen in Argentina by Cabot in 1530 were indi- 

 genous (and it is very difficult to. understand how they 

 could have been introduced'), they must certainly have 

 been Onohippidiums. Could my correspondent's horse 

 have been one of their cross-bred descendants? 



•"The Origin of the Thoroughbred Horse.' 

 bridge Phil. Soc . vol cxi . pp 141-14J (1Q03). 



I'roc. Cam- 



Photography. 



Pvire a^rvd Applied. 



By Ch.'vpm..\n Jones, F.I.C, F.C.S., &c. 



Reversal Further Considered.— There is_ no room 

 for doubt that the developable condition is of 

 a more complex character than it is often sup- 

 posed to be. Sir William .^bney showed some 

 years ago that the result was not uniform, although the 

 time of exposure multiplied by the intensity of the light 

 was constant, if the light intensity varied— that is, the 

 result of the action of an intense light for a short 

 period is not the same as that of a weak light for an 

 equi\alent longer time. The action seems to me to be 

 comparable to the difference between the few blows of 

 a heavy hammer and the many blows of a light 

 hammer, though I do not wish to suggest that the 

 analogy is complete. The different effects produced by 

 various forms of radiant and other energy are more 

 especially noticeable when the action is allowed to pro- 

 ceed beyond what would produce a normal result, or 

 when one kind of energy is allowed to follow another. 

 Professor R. W. Wood has distinguished five " types " 

 of reversal (better, perhaps, called met/tods of reversal), 

 namely : (i), ordinary over-exposure, the same light 

 being allowed to continue to act ; (2), reversal pro- 

 duced by developing the plate while it is illuminated liy 

 lamp-light or feeble daylight ; (3), the result of exposure 

 for a minute or two to light between developing and 

 fixing ; (4), the Clayden effect, a longer feeble exposure 

 following a short intense exposure ; (5), reversal pro- 

 duced by treating an exposed plate with a solution of a 

 bichromate containing nitric acid, drying, and fogging 

 by exposure to candle-light before developing. Pro- 

 fessor Wood also found that Rontgen rays prevent the 

 reversal of spark images by candle-light, that is, they 

 negative the Clayden effect ; but that the normal effect 

 of Rontgen ravs c;ui be reversed by lamp-light. He 

 arranges the following methods of producing the de- 

 velopable effect in order : (i), pressure marks ; (2), 

 Rontgen rays ; (3), light shock (that is, an intense 

 light acting for a short time, one-thousandth 

 of a second or less) ; (4), lamp-light ; and finds 

 that any one can be reversed by subsequent ex- 

 posure to any other that follows it in the list, but not 

 Ijy any that precedes it. Mr. Skinner has since ob- 

 served that radium will reverse electric spark images 

 (analogous to the Clayden effect), and by prolonging 

 the exposure actually obtained a re-reversal. It has 

 been stated that the continued application of Rontgen 

 rays will not produce reversal. I do not know of any 

 record of reversal produced by pressure. Perhaps the 

 first three methods of producing the developable effect 

 given above are unable to cause reversal of the normal 

 result produced by each respectively. We want an 

 experimental investigation of these and similar matters 

 made under more definite conditions than any th.at have 

 yet been published. 



An Effect of Colour Screens. — A question that has 

 been mooted occasionally, is as to whether a colour 

 screen causes the light that it transmits to produce a 

 greater effect (in the production of a developable 

 image) than the same light would without the screen, 

 when for example, the spectrum is photographed. 

 General Waterbouse recently stated that he had found 

 a chrysoidin screen to .apparently confer greater sensi- 

 tiveness to red than the unscreened plate showed. 



