6io 



NATURE 



[July 15, 1920 



the greatest fundamental importance. With the 

 curve are, of course, included the units that it 

 involves and the facts that it represents. As to 

 its advantages, it is enough to say that it was at 

 once adopted wherever photography was regarded 

 as a science, and no better method of expression 

 has since been suggested. 



Their second notable achievement was that 

 they promulgated certain conclusions to which 

 they had come with an energy and assurance that 

 stand unique in connection with this, if not 

 with all scientific subjects. Their statements in 

 their communication of 1890 with regard to some 

 of the opinions and experiences of others as inter- 

 ested in the subject as they were, were put in such 

 vigorous language that they amounted to chal- 

 lenges. Of course, this led to discussion and to 

 further work ; and discussion breeds discussion, 

 and work breeds work. Df. Hurter and Mr. 

 Driffield either separately or jointly were always 

 ready to take any pains, by reading papers, 

 often travelling long distances to do so, by writ- 

 ing articles, or by personal correspondence, to 

 make clear and to uphold their views. They thus 

 administered a powerful stimulant to scientific 

 photography. 



It is of very secondary interest what these views 

 were, because the whole subject has received since 

 then more attention than any two persons could 

 possibly devote to it; and, indeed, Hurter and 

 Driffield themselves, in their last important com- 

 munication on "The Latent Image and its De- 

 velopment," demonstrate by further experiments 

 the necessity of largely, if not radically, modifying 

 the statements to which so much exception had 

 been taken. 



It must not be supposed that Hurter and 

 Driffield set out with the intention of doing the 

 two things that we have endeavoured to describe. 

 To quote their own words : " Our object was to 

 discover a method of speed determination, and 

 it was not, as the [photographic] public seemed to 

 infer, to deal finally and exhaustively with the sub- 

 ject of development. This subject was purely inci- 

 dental. ..." As everyone knows, they did devise 

 a method for the estimation of sensitiveness, and, 

 as might be expected from such capable men, a 

 method wholly different from any other, but, like 

 all methods, it has its advantages and its disad- 

 vantages. The sensitiveness of a plate is not de- 

 finite except under definite conditions, and in prac- 

 tical work the conditions are not uniform. 



It is but a short step from the courteous and 

 ever kindly Hurter and Driffield to the memorial 

 volume before us, because Mr. Ferguson has done 

 his work well and with full sympathy. The 

 volume begins with Mr. Ferguson's recent lecture 

 NO. 2646, VOL. 105] 



on their early work, which is followed by a review 

 of Dr. Hurter's mathematical work by Dr. H. 

 Stanley Allen, and by the patent specifications of 

 the early actinometer and the actinograph. Then 

 come reprints of all their important communica- 

 tions to societies and journals. Mr. Ferguson has 

 certainly not erred in the direction of rnaking too 

 exclusive a selection, though he tells us that there 

 are many other publications of theirs, chiefly 

 polemical letters to the photographic Press, which,, 

 if reproduced, would have filled two more volumes. 

 After this there are a bibliography of 717 items, 

 extending from 1881 (Hurter's actinometer patent) 

 and 1888 (the actinograph patent) to 1918, and 

 name and subject indexes. If there should exist 

 anyone interested in scientific photography who is 

 so saturated with the work of Hurter and Driffield 

 that the reprints do not appeal to him, even he 

 cannot fail to find the bibliography and indexes of 

 considerable use. C. J. 



Our Bookshelf. 



Bygone Beliefs: Being a Series of Excursions in 

 the Byways of Thought. By H. Stanley Red- 

 grove. Pp. xvi + 205 + 32 plates. (London : 

 William Rider and Son, Ltd., 1920.) Price 

 I05. 6d. net. 



This series of fragmentary discussions extends 

 over a vast area : Pythagoras and his philosophy, 

 medicine and magic, bird superstitions, powder 

 of sympathy, talismans, ceremonial magic, archi- 

 tectural symbolism, the Philosopher's Stone, the 

 phallic element in alchemical doctrine, Roger 

 Bacon, and the Cambridge Platonists. It is in- 

 evitable that a discussion of such varied subjects 

 in a limited space is not likely to be fruitful, nor 

 will the author's interpretations command uni- 

 versal acceptance. Thus we are told that "the 

 alchemists regarded the Philosopher's Stone and 

 the transmutation of the base metals into gold as 

 the consummation of the proof of the doctrines of 

 mystical theology as applied to chemical pheno- 

 mena," though some were influenced by more 

 material objects. The premises from which they 

 started were "the truth of mystical philosophy, 

 which asserts that the objects of Nature are 

 symbols of spiritual verities. There is, I think,, 

 abundant evidence to show that alchemy was a 

 more or less deliberate attempt to apply, accord- 

 ing to the principles of analogy, the doctrines of 

 religious mysticism to chemical and physical 

 phenomena." Of course, it is generally admitted 

 that the idea of transmutation had a philosophical 

 basis such as it was, and that alchemy to some 

 extent unified and focussed chemical effort, but it 

 was, to use Liebig's words, "never at any time 

 anything different from chemistry." 



While it is difficult to accept the author's tran- 

 scendental interpretations of these and kindred 

 phenomena, he has collected much curious learn- 

 ing, for which he supplies adequate references,. 



