May 28, 1896J 



NA TURE 



77 



Becquerel's and Lippmann's Colour Photographs. 



TiiF. point raised by Prof. Mcldola (|i. 2S( is partially, if not 

 completely, answered by Otto Wiemr in a most valuable 

 paper, " Ueber Farbenphotograihie liiirch Korperfarben, und 

 Mechanische Karbenanpassung in der Xatur," published in 

 Wiedemann's Annakn, 1895, Iv. 225-2S1. Wiener devised a 

 method of examining colour photographs through a right-angled 

 prism in such a way that pigment colours, which owe their hues 

 to absorption, are distinguished from interference colours by not 

 changing their positions when seen through the prism. The 

 application of this method to colour photographs by Lippmann's 

 process and the older processes of Seebeck, Poitevin and 

 Becquerel, shows that in Lippmann's photographs the colours 

 are due entirely to interference. In feccquerel's process they 

 are due mainly to interference, though pigment colours are 

 formed to an extent which is generally very small, but which 

 increases with the duration of the ex]io5ure. The colours on 

 Becquerel plates do change with the angle of incidence, though 

 the changes are very small, probably in con<^equence of the high 

 refractive power of the film. Further, when the film is examined 

 from the back the colours do not occupy the same positions as 

 when they are viewed from the front. It follows that the colours 

 on Becquerel plates are due essentially to the same cause as 

 those on Lippmann's plates, and the theory of standing wave.s is 

 applicable in both cases. 



With the processes of Seebecic and of Poitevin, on the other 

 hand, the colours are exclusively pigment colours, and the 

 theory of standing waves is not applicable. 



Weston-super-Mare, May 16. C. H. Bothami.ey. 



Influence of Terrestrial Disturbances on the Growth of 

 Trees. 



In reply to the note of Mr. H. J. Colliourn on "Influences 

 of Terrestrial Disturbances on the Growth of Trees," in your 

 issue of Ajiril 23, allow me to say that his ingenious suggestion 

 of connecting a zone of narrow rings in a section of Douglas 

 spruce with some supposed terrestrial disturbances occurring 

 about the same time, is hardly tenable, even if the coincidence 

 of the two phenomena were established, which seems not to be 

 the case. The occurrence of a zone of narrow rings is common 

 in all our trees, and I have observed it most frequently in all 

 southern pitch pines, which are rarely over three hundred years 

 old, and hence outside of the possibilities of the influence of 

 unknown or uncertain terrestrial disturbances. 



The suddenness with which the rings become narrow and then 

 again wide, described by Mr. Colbourn, and observed by us in 

 many other trees, is, to be sure, puzzling ; nevertheless, we cannot 

 escape the conclusion that it is due to changes in the conditions 

 surrounding the tree. Vet it is not necessary that the change of 

 conditions and of ring-width should be sinndtaneous, that is to 

 say, the change of conditions may have occurred without having 

 been immediately responded to by the growth of the tree. 



The following explanation may serve as a type. Let a tree 

 grow up under favourable conditions for a hundred years, as the 

 Douglas spruce in question seems to have done, when its ring- 

 growth will be wide, its crown reaching aliove its neighbours. 

 A hurricane breaks off a large part of its crown, when necessarily 

 and suddenly, at least within a year, the rings become narrow in 

 proportion. Within the next thirty years the crown recuperates, 

 which in a resinous conifer like the Douglas sprtice is possible 

 without fear of fungus attacks and decay : liut the food-material 

 descending from the foliage will for a long time be only sufficient, 

 on the particular section in question at the base of the tree, to 

 make the narrow annual ring, even afti-i the crown is fully 

 recu])erated. Were a section cut higher up in the tree, it would 

 be found that the rings there have begun to widen sooner than at 

 the lower section. Finally, and rather suddenly for any given 

 section, the supply has become normal, and especially if an 

 exceedingly favourable season occurs at the same time the rings 

 show again normal width. 



The same sudden change from narrow to wide rings is observed 

 when a tree oppressed by its neighbours is suddenly relieved by 

 windfall or by man's interference from its oppressors; but the 

 response even then is not simultaneous, it takes one or more 

 years before the crown is in condition to utilise the full amount 

 of light at its disposal, and to furnish food lo all parts of the tree 

 in increased ratio. B. E. Fernow. 



Washington, D.C., May 11. 



NO. 1387, VOL. 54I 



Our Bishops and Science, 



The friends of both science and religion will thank you 

 warmly for publishing the Bishop of Ripon's public testimony 

 to Huxley's spirit of sincerity and love of truth. It is the more 

 timely becau.se of your recent strictures upon the Bishop of 

 London. May I therefore, as a country parson, with an equal 

 love for scientific integrity and religious truth, suggest to the 

 readers of those strictures in N.vrURE (p. 607, April 30) that 

 probably Bishop Temple has been misunderstood. I am sure it 

 is not fair to his spirit to put into his mouth, " Away with all 

 these abominations. Purge the elementary schools of everything 

 scientific, and substitute dogmas and subjects more fitted to the 

 stations of life in which it has pleased God to call the scholars." 



Is it not more likely that the real clue is in the sentence 

 quoted about "instructing little children m ckmcntar)"i,z\\on\% 

 in a great many scientifi< subjects ? " For many earnest edu- 

 cationalists have, as friends of science, spoken strongly on 

 the evils of the cramming of bits of science subjects and 

 "stages" by crudely crammed "Government certificated" 

 "science" teachers cramming large classes for grants on 

 " passes" to butter their bread. 



In any case, the true views of the great bishop will be found 

 in his " Bampton Lectures" for 1S84, on the relations between 

 science and religion ; and the last Quarterly Review, on G. J. 

 Romanes, contains an eminent example of the reverent treat- 

 ment of both. 



I will frankly add that I do not think your quotations from Mr. 

 Mundella's address can be too widely known among the bishops 

 and clergy who have such influence with the laity. Agricultural 

 pursuits suffer more from our ignorance than our want of money ; 

 and agricultural science cannot be widely taught until the 

 elementary principles of chemistry and physics are diffused in our 

 villages. 



On this subject we have also had the weighty testimony of 

 Mr. Gladstone. The voting of money for light railways and 

 such objects is a quack remedy. The fact is that true edu- 

 cational enthusiasts who will think first of our children, and be 

 generous to \}cvexa first, have hitherto been appallingly scarce in 

 the House of Commons and its parties. 



Nor is even the geographical significance of our need of science 

 education likely to be perceived by the majority, if, as is stated 

 in the Anti-Slavery Reporter (March-April 1896, p. 80), two 

 M.P.scan stand before a map of South America in the map 

 room of the House of Commons, and dispute with one another 

 as to where Egypt was to be found on that map. However 

 matters are mending, we hope. J. F. Heyes. 



Crowell, Oxon, May 15. 



Blood-Brotherhood. 



There are good reasons why this ancient custom can never be 

 a preventive of disease, though sometimes it may be a cause of 

 it. The serum treatment has been found useful, and presumably 

 will be found useful only in such diseases or diseased conditions 

 as are due to poisons (toxins) secreted by various species of 

 pathogenic micro-organisms (e.g. those of rabies, anthrax, 

 diphtheria), or by some animals {e.g. scorpion, snake), as 

 weapons of offence or defence. 



As regards certain zymotic diseases {e.g. small-pox, scarlatina, 

 syphilis), it is known that one attack confers more or less 

 complete immunity against subsequent attacks ; that is, the 

 micro-organisms of these diseases are, after the recovery of the 

 host, unable to persist and produce their toxins in him ; and this 

 for the reason that during his illness certain of his body cells, 

 known as phagocytes, become inured to the toxins, and are thus 

 enabled to attack and destroy the micro-organisms producing 

 them. When the phagocytes fail to become inured, the micro- 

 organisms continue to produce these toxins, and the host 

 perishes, poisoned by them. Now the toxins produced by the 

 micro-organisms of most zymotic diseases are not always of the 

 same degree of virulence, and when they are feeble the phago- 

 cytes the more easily become inured to them, and destroy the 

 micro-organisms ; and not only do they do so, but this pre- 

 liminary training enables them, when attacked by more virulent 

 micro-organisms of the same species, i.e. of the same disease, to 

 react to the stronger toxins of these also, and again destroy the 

 micro-organisms. Man has taken advantage of this fact to 

 artificially lower or "attenuate" the virulence of various species 

 of pathogenic micro-organisms {e.g. those of anthrax an 



