July i8, 1895J 



NATURE 



279 



potato and roots, leaves, &c. — to be eaten at ease in the 

 seclusion of the animals' burrows, or to be stored up for use in 

 the winter. The food is passed into the pouches liy the fore- 

 feet : and the animals empty their pockets by pressing the sides 

 of the head with the fore-feet from behind forwards, so that the 

 contents fall out in front of them. In disposition (lophers are 

 verj' fierce : and on the rare occasions on which they wander 

 from their holes, frequently attack passers-by without any pro- 

 vocatii)n. They are not very prolific animals, as is commonly 

 stated, for only one litter of two or three young is ])roduced in 

 a year ; but, although their rate of increase is slow, their mode 

 of life ]5ro'.ects them from many enemies which attack squirrels, 

 mice, and many other rodents. The I'ocket (iophers of the 

 United States belong to three genera, Geoiiiys, Cratogeoiiiys, 

 and Tlwmomys : Mr. Bailey gives two charts illustrating 

 the distribution of these different genera and their constituent 

 species. 



COLOUR PHOTOGRAPHY. 

 A N important paper on the theory of colour photography is 

 ■^ *- contributed to No. 6 of Wit'demann" s Annalen, by Herr Otto 

 ^Viener. The paper deals with the methods of attacking this 

 problem which are based, not upon the photography of the dif- 

 ferent constituents of coloured light and their subsequent re- 

 cognition — like Mr. Ives's heliochromy and similar processes 

 -—but upon the direct production of colour by the influence 

 of light upon certain chemical substances. The most recent, 

 .ind in a way the most successful of these methods is that due 

 : i Lippmann. and the question raised by Herr Wiener is whether 

 ihe old processes invented by Becquerel, Seebeck, and Poitevin 

 are based upon interference colours like Lippmann's, or upon 

 *' body colours," ?.t'. colours produced by partial absorption of 

 the incident light. That Lippmann's colours are due to inter- 

 ference may be very simply proved by breathing upon a plate 

 with a iihotf>graph of the s])ectrum, when the colours quickly 

 wander towartis the violet end, this result being due to an in- 

 crease in the distance between the nodal layers. This experi- 

 ment cannot be applied to a spectrum photographed by 

 Becquerel's method. But Herr Wiener succeeded, t)y a simple 

 and ingenious contrivance, altering the path of the rays thr^)ugh 

 the coloured film by placing a rectangular prism on the jilate, 

 with its hypolhenuse surface in contact with the spectrum. This 

 experiment had the startling result that that part of the spectrum 

 covered iiy the prism a]5peared strongly displaced towards the 

 red. Hence Zenker's theor}' of Becquerel's process, enunciated 

 in 1868, which ascribed the colours to interference, is substan- 

 tiated. Instead of Becquerel's homogeneous sheet of silver 

 chlfjride containing subchloride, Seebeck used the powder, and 

 I'oitevin nu>unted the salt on paper. In these two processes the 

 1 tfect described is not observed. Hence these colours are body 

 colours in these two cases. The j^roduction of these body colours 

 is a very mysterious process, but the author hopes that here will 

 eventually lie found a satisfactory solution of the problem. To 

 account for the |iroduction of these colours he advances a remark- 

 able theory which has a well-known analogy in comparative 

 physiology, (iiven a collection of compounds of silver chloride 

 and subchloride of indefinite proportions, such as those which 

 Mr. Carey Lea calls by the collective name of " photochloride," 

 we must suppose according to the modern kinetic theories that 

 they are undergoing a rapid series of successive modifications. 

 When the red combmation happens to be exposed to red light, it 

 reflects it without absorption, and will therefore no longer be 

 aftected or changed by it. Similarly for the other cases. This 

 is another process of " adaptation.'' The author describes some 

 experiments which jirove that this is the true explanation, and 

 points out the importance of this view, not only for colour ])hoto- 

 graphy, but for the production of colours in the animal world. 



THE SLATE MLNES OF MERLONETHSHIRR} 



AN official Blue Book drawn up by a Departmental Committee 

 ^^ appointed by Mr. Asquith, and referring to the dangers of 

 slate quarrying in Merionethshire, has recently appeared, .\fter 

 a brief account of the mode of occurrence, the method of getting 

 the slate by true mining operations is described, and the principal 



' Report of the Departmetu.iICominittee upon Merionethshire Slate Mines. 

 with Appcndic.-s. Presented to lioth Houses of Parliament by command of 

 Her Majesty, 1895. 



NO. 



1342, VOL. 52] 



causes of accidents are enumerated and explained. Judging by 

 the statistics of the last nineteen years, the underground worker 

 in Merionethshire is exposed to greater risks than the average 

 collier; some 40 per cent, of the deaths are caused by falls of 

 rock, a fact which causes no surprise when one considers the 

 conditions under which the slate-getters carry on their daily work 

 in huge chambers, the roofs and sides of which cannot be 

 examined without rigging up lofty ladders. 



An interesting table of death-rates shows that the Merioneth- 

 shire slate quarrymen are better off as regards the safety of their 

 occupation than many other classes of workmen, such as navvies, 

 railway servants, and sailors. 



The medical evidence, especially that of Dr. Richard Jones, 

 is very complete, and we learn that some of the ills of the 

 Merionethshire quarrymen are practically of their own making. 

 Judging by the report and the evidence upon which it is based, 

 the men are not cleanly in their ways, and if their sober habits 

 lead them to ruin their digestions by stewed tea, it becomes a 

 question whether their so-called, but incomplete, temperance is 

 an unmixed benefit. 



For preventing accidents, the Committee make several useful 

 suggestions ; one of the most important is their advocacy of 

 "channelling machines" or "groove cutters," for assisting in 

 getting the slate, instead of \-iolently wrenching off the blocks by 

 blasting. 



The value of the report is enhanced by some useful ayipendices, 

 a copious index of the evidence, and several woodcuts and plates. 

 The plates are noteworthy as being the first instances of repro- 

 ductions of photographs in a Blue Book by the half-tone process. 

 Five of the eight photographs were taken underground by 

 magnesium light ; the two best, which represent ladders set up 

 in underground chambers, are the work of Mr. Burrow, of 

 Camborne, already well known by his successful pictures of 

 Cornish mines. 



The report is signed by Mr. Le Neve Foster, the Inspector of 

 Mines of the district, Mr. J. E. Greaves, the owner of one of 

 the largest slate mines, Mr. E. ;P. Jones and Mr. J. J. Evans, 

 both quarry managers of wide experience, and Mr. J. Jenkins, 

 President of the (Juarrymen's Union. The opinions of a practical 

 Committee of this kind are entitled to consideration, and it will 

 be interesting to note how far their suggestions are carried out, 

 and how far they attain their object, viz. the increased safety 

 and general well-being of the Merionethshire quarrymen. 



THE RE LA TLON OF BIO LOG Y TO GEO- 

 LOGICAL INVESTIGATION > 



II. 



The Riii..^rivE Chronological Value of Fossil Kk.mains. 



■p EJECTING the idea of special endowment held by early 

 geologists, we must consider the relative chronological value 

 of fossil remains with reference to the natural laws which have 

 produced their characteristics and governed the various conditions 

 of their origin. .Much may profitably be .said concerning the 

 comparative chronological value of the difterent genera, families, 

 lie, belonging to one and the same class of any liranch of 

 either the animal or vegetable kingdom, or to difl'erent classes ; 

 but I propose to discuss only the broader relations to one 

 another of the more general kinds of fossil remains. These 

 discussions will relate to the time-range of each of those general 

 kinds, the various conditions under which they have been 

 preserved, the various conditions of habitat of the animals and 

 plants which they rejiresent, the relative rate of e\(ilutional 

 develoi)ment of the different kinds and their diflerences of 

 reciprocal relation to one another. 



No fact in historical geology is more conspicuous than that 

 of the great diflerences in time range of the various kinds of 

 organic forms, some of them having ranged through the whole 

 of the time represented by the geological scale, while others, 

 and among them some of the biologically most important kinds, 

 ranged through only a comparatively small part of it. 



.■\ special grouping of the diflferent kinds of fo.ssil remains is 

 more appropriate for these discussions than is a strictly systematic 

 one, and I have therefore adopted the following : (a) marine 

 invertebrates, (b) non-marine antl land invertebrates, (r) fishes. 

 ((/) batnachians and reptiles, (c) birds, (/) mammals, and 



1 By Charles .\. White. .Abstract of a scries of ciRht cs.savs published in 

 the Report of the t^'iiited States National Museum. (Continued from p. 261. 



