lOO 



NATURE 



\May 23, 1878 



one occasion it will select one outline, on another a dif- 

 ferent one. Looking at the patterns of the papered walls 

 of our room we see, whenever our fancy is active, all 

 kinds of forms and features ; we often catch some strange 

 combination which we are unable to recall on a subsequent 

 occasion, while later still it may suddenly flash full upon 

 us. A composite portrait would have much of this 

 varied suggestiveness. 



A further use of the process would be to produce from 

 many independent portraits of an historical personage, 

 the most probable likeness of him. Contemporaneous 

 statues, medals, and gems would be very suitable for the 

 purpose, photographs being taken of the same size, and a 

 composite made from them. It will be borne in mind 

 that it is perfectly easy to apportion different " weights " 

 to the different components. Thus, if one statue be judged 

 to be so much more worthy of reliance than another that 

 it ought to receive double consideration in the composite, 

 all that is necessary is to double either the time of its 

 exposure or its illumination. 



The last use of the process that I shall mention is of 

 great interest as regards inquiries into the hereditary 

 transmission of features, as it enables us to compare the 

 average features of the produce with those of the" 

 parentage. A composite of all the brothers and sisters in 

 a large family would be an approximation to what the 

 average of the produce would probably be if the family were 

 indefinitely increased in number, but the approximation 

 would be closer if we also took into consideration those 

 of the cousins who inherited the family likeness. As 

 regards the parentage, it is by no means sufficient to take 

 a composite of the two parents ; the four grandparents 

 and the uncles and aunts on both sides should be also 

 included. Some statistical inquiries I published on the 

 distribution of ability in families^ give provisional data 

 for determining the weight to be assigned in the composite 

 to the several degrees of relationship. I should, however, 

 not follow those figures in the present case, but would rather 

 suggest for the earlier trials, first to give equal "weights" 

 to the male and female sides ; thus the father and a 

 brother of ,the male parent would count equally with the 

 father and a brother of the female parent. Secondly, I 

 should " weight " each parent as 4, and each grandparent 

 and each uncle and aunt as i ; again, I should weight each 

 brother and sister as 4, and each of those cousins as i 

 who inherited any part of the likeness of the family in 

 question. The other cousins I should disregard. The 

 weights as previously mentioned, would be bestowed by 

 giving proportionate periods of exposure.* 



Composites on this principle would undoubtedly aid the 

 breeders of animals to judge of the results of any proposed 

 union better than;they are able to do at present, and in for- 

 casting the results of marriages between men and women 

 they would be of singular interest and instruction. Much 

 might be learnt merely by the frequent use of the double 

 image prism, as described above, which enables us to 

 combine the features of living individuals when sitting 

 side by side ioto a single image. 



I have as yet had few opportunities of developing the 

 uses of the composite photographic process, it being 

 difficult without much explanation to obtain the requisite 

 components. Indeed, the main motive of my pubhshing 

 these early results is to afford that explanation, and to 

 enable me to procure a considerable variety of materials 

 to work upon. I especially want sets of family photographs 

 all as nearly as possible of the same size and taken in the 

 same attitudes. The size I would suggest for family 

 composites is that which gives one-half of an inch interval 

 between the pupil of the eye and the line that separates 



^ "Henditary Geniu?,"p. 317. Column D. Macmillan, 1869. 



Example : — There are 5 brothers or sisters and 5 cousins whose portraits 

 are available ; the total period of desired exposure is 100 seconds. 5 X 4+5=25 ; 



25 ^' which gives 4 X 4 = 16 seconds for each brother or sister, and 4 



-seconds for each cousin (5 X 16 + 5 x 4 = 100). 



the two lips. The attitudes about which there can be no 

 mistake are : full face, an exact profile, say, always show- 

 ing the right side of the face, and an exact three-quarters, 

 always showing the left ; in this, the outer edge of the 

 right eye-lid will be only just in sight. In each case 

 the sitter should look straight before him. Such portraits 

 as these go well into cartes de visite, and I trust that not 

 a few amateur photographers may be inclined to make 

 sets of all the members of their family, young and old, 

 and of both sexes, and to try composites of them on the 

 principles I have described. The photographs used for 

 that purpose need not be in the least injured, for the 

 register marks may be made in the case into which they 

 are slipped, and not in the photographs themselves. 



THE SEICHES OF THE LAKE OF GENEVA ' 



AMONG the best-established phenomena of terrestrial 

 physics is that which from ancient times has been 

 known at Geneva under the name of seiches. Its true 

 nature has been only recently recognised, and the ob- 

 scurity which still envelops its causes gives it an interest 

 calculated to attract the attention of men of science of 

 every country. It is not necessary to have a knowledge 

 of science to recognise in the neighbourhood of Geneva 

 sudden irregular changes of very varied amounts, which 

 sometimes affect the level of the lake. They are analo- 

 gous to small tides whose existence is well established, 

 but whose origin is not determined. For eight years 

 Prof. Forel has worked at the problem by studying the 

 characteristics of the progress of the phenomenon. The 

 following is a rhume of his observations and conclusions. 



Previous to Prof. Forel, eminent naturalists, among 

 them Jallabert, Bertrand, H. B. de Saussure, J. P. E. 

 Vaucher, had pointed out the existence of these seiches, 

 described them, and hazarded hypotheses to account for 

 them, hypotheses which for the most part cannot be 

 maintained. Former observations furnish some guiding 

 points to examine the question. They were made mainly 

 near Geneva, where the oscillations of the level of the 

 lake are much more marked than anywhere, else on its 

 shores. It is, however, at a much less favourably situated 

 point of the shore that M. Forel has undertaken his 

 regular investigations. Merges, his usual residence, is 

 situated on the north shore of the lake, opposite its 

 greatest breadth, and a little to the east of the line divid- 

 ing its total length into two equal parts. There, by means 

 of ingenious instruments, the movements of the liquid 

 surface have been registered with regularity and sagacity, 

 and veritable discoveries have been the result of the 

 work. 



Vaucher, at the beginning of the century, had already 

 surmised that seiches must exist in all lakes, that they 

 take place at all seasons and at all hours of the day, that 

 they are more frequent in spring and in autumn, more 

 frequent especially when the atmosphere is subject to 

 strong variatious in pressure. He valued approximately 

 their duration, and predicted their character of per- 

 manence, which assimilated them to the incessant oscil- 

 lations of the fluid mass. He believed, as H, B, 

 De Saussure announced in 1779, that "prompt and local 

 variations in the weight of the air could contribute to the 

 phenomenon and produce momentary fluxes and refluxes 

 by causing unequal pressures on the different parts of the 

 lake," The movement of the liquid will then be an oscil- 

 lation of libration. Vaucher admitted that this oscillation 

 was progressive. His conclusion did not appear justi- 

 fied ; he did not take into account the rhythm of the 

 seiches, which, in reality, shows itself with a remarkable 

 regularity whatever be their amplitude, and the duration 

 of which is connected with the dimensions of the lake in 

 length and depth. 



' Researches by Dr. F. A. Forel, Professor at the Academy of T au- 

 sanne. Bulletins de la Section Vqudoise des Sciences Natureiles, 1873 and 

 1875. Arch, des Sc, 1874-76. 



