Supplement to ''Nature," March 5, 1908 



which must furnish Ihe terms of ultimate analysis 

 and are led to the discovery of the impressive 

 continuity as existent between the responses of the 

 most complex living and the simplest inorganic 

 matter." 



Sensibility is the power to feel, and is the function 

 of the cerebral cortex of man, and also, we liiay 

 assume justly from the similarity of the neuro- 

 muscular reactions, the function of the brain of the 

 higher animals. That it is a function of the fish or 

 frog brain we cannot affirm with any certainty. To 

 ascribe it to a plant or wire is altogether unwarrant- 

 able. 



.\ similar condition of molecular strain may be 

 present in a wire, a plant stem, and a nerve fibre, 

 and give the same electrical response, but this is not 

 sensibility, and we even cannot conclude justly from 

 the similarity of electrical response that the same 

 mechanism is present. 



Suppose we see a cloud of steam rising over the 

 wall of a field. It may be from a traction engine, 

 from a dung heap, or from a team of horses heated 

 with ploughing. Observations on the direction of 

 the current of steam, and on the effect of modifying 

 agents upon it, will tell us nothing as to the nature 

 of the chemical process which results in the mani- 

 festation of heat and the evaporation of water. Prof. 

 Bose's philosophy seems almost capable of asserting 

 that the similarity in direction of the steam current 

 proves the sensibility, not only of the horses, but of 

 . all three structures. 



Apart from these criticisms, there are in Prof. 

 Bose's book a great many very interesting 

 observations and ingenious methods of experimentation 

 which will repay the reader's attention. In parti- 

 cular, his experiments on root pressure and the rise 

 of sap ; those by which he seeks to demonstrate that 

 not only sensitive plants but all plants respond to excit- 

 ation by variatio.is in turgescence and electrical state ; 

 his comparison of the glandular structures of sundevt- 

 and pitcher plants with animal glands ; his demon- 

 stration of Dr. Waller's " blaze current " in a 

 brominated lead plate and assertion that it cannot 

 be regarded as a sign of life ; his demonstration on 

 the motile leaflets of Biophytum of the anodic and 

 kathodic effects of the constant current, and the 

 velocity of transmission of excitatory waves ; his 

 comparison of retentiveness of molecular change 

 in metals \vith memory. In fact, the whole book 

 abounds in interesting matter skilfully woven 

 together, and would be recommended as of great 

 value if it did not continually arouse our incredulity. 



L. H. 



THE STEREOSCOPE AND STEREOSCOPIC 

 INSTRUMENTS. 

 Die hinokidarcn Instrumcnte. By Moritz von Rohr. 

 Pp. viii + 223. (Berlin : Julius Springer, 1907.) 

 Pricf 6 marks. 

 'T^HK scientific staff of the Zeiss firm have of late 

 -*- years devoted much attention to the theory of 

 binocular instruments, and to the development of 

 method- of measurement depending on stereoscopic 

 NO. 2001, VOL. jy'] 



vision. The impetus given by the successful realisa- 

 tion of the prism field-glass has carried them on to 

 a more exact examination of the conditions under 

 which binocular vision can be emploj'ed for the accu- 

 rate determination of relative position, which has led 

 to the design of a series of new instruments for sur- 

 veying and other purposes, of which the stereo- 

 comparator is the most widely known. 



The thoroughness with which the problem has been 

 considered is sufficiently illustrated by the present work 

 of von Rohr, w-ho has already in his previous writ- 

 ings dealt very completely with the theory of vision 

 by means of binocular instruments. This previous 

 work he has now supplemented with an examination 

 into the historical evolution of stereoscopic instru- 

 ments, systematically planned with the view of clear- 

 ing the ground and avoiding loss of labour from the 

 re-development of ideas already investigated by pre- 

 vious workers. The book is divided into three parts ; 

 the first gives in a few pages a concise statement of 

 the theory; then follows the history, to which part i. 

 is merely an introduction ; and the volume concludes 

 with a most useful systematic summary of the matter 

 contained in part ii., assisted by what may be described 

 as a logical guide arranged in the form of a genea- 

 logical table, showing the subdivisions of the subject 

 and referring to the place of treatment. This third 

 part, of course, includes a bibliography. 



The history begins seriously with the work of Ch. 

 Wheatstone, who is even better known as an elec- 

 trician. Reference is indeed made to some previous 

 writers and instruments, from the early binocular of 

 Lipperhey, and the suggestive experiments of R. 

 Smith. One notices some omissions here, but the 

 book makes no pretence to be exhaustive ; the object is 

 only to trace out the development of correct principles 

 of construction, and to indicate the most important 

 workers and the advances due to them. From this 

 aspect the book is almost too thorough and complete. 



Much soace is devoted to the famous controversy 

 between Sir David Brewster and Wheatstone, again 

 because of its value for the development of the theor\ . 

 It is now generally recognised that Wheatstone had 

 the much more correct grasp of the principles, and 

 that the popularity of the Brewster type of prism 

 stereoscope as against the Wheatstone mirror instru- 

 ment was due to its superior handiness, which out- 

 weighed its optical deficiencies. It is interesting to 

 note that Brewster records the sale of prism stereo- 

 scopes from the time of the Great Exhibition to 1856 

 as amounting to more than half a million ; these for 

 the most part on the improved mechanical design of 

 Duboscq. One can still remember the wide interest 

 aroused by this method of obtainmg pictures in relief. 



The interest, however, soon died down, only to be 

 revived in comparatively recent years. The simple 

 stereoscope was gradually improved, as well as the 

 binocular microscope, and more especially the bino- 

 cular field-glass. The advances of photographj' were 

 accompanied by the invention of various methods of 

 obtaining " stereograms." But public interest only 

 I revived with Abbe's introduction of the prism bi- 

 nocular. Since then Jena has been the centre for the 

 spread of renewed enthusiasm for the subject, while 



