NA TURE 



[June 4, 1896 



more to be apprehended and appreciated- the theory lay 

 which they have been obtained. 



In the chapter on the "Dimensions of Electrical 

 Quantities," the author introduces besides u and K a 

 third constant/, which may arise in connection with the 

 relation between the current and the magnetic intensity 

 at any point in the field produced, so that 4rr times the 

 current flowing through a closed path in a magnetic 

 field is equal to/ times the work done in carrying a unit 

 pole once round the path. The dimensions of this 

 constant are of course unknown, and it is only by 

 assuming its dimensions to be zero that the ordinary 

 dimensions of current in electromagnetic units are 

 obtained. There does not seem any distinctly physical 

 ground for bringing in this constant p. The work done 

 in canning a pole in a complete circuit round a current 

 is independent of the nature of the medium, and hence, 

 justifiably so far as we can see, it may be taken as unity, 

 without involving any neglect of the physical properties 

 of the medium. 



The method of the motion of Faraday tubes of electric 

 induction is used in the chapter on " Dielectric Currents 

 and the Electromagnetic Theory of Light." Perhaps it 

 is possible to make too much of this conception ; but 

 there can be no question of its great utility as a means 

 of keeping before the mind of the reader the idea of 

 electric and magnetic action as taking place in the 

 medium, and visualising, as it were, what takes place 

 when a condenser is joined to another and partially dis- 

 charged, when a current flows in a circuit, and the flux 

 of energy in the medium which accompanies all such 

 changes, whether constant or rapidly variable. 



The commendation which the work of Prof. J. J. 

 Thomson thoroughly deserves is the due also of that 

 which Prof. Carey Foster and Dr. Atkinson have based 

 on the elementary treatise of M. Joubert. This work 

 has been recast so as to bring it thoroughly into 

 accordance with the later views of electrical theory, and 

 there can be no question of the entire success with which 

 the English authors have performed their task. The 

 book is a thoroughly sound and practical treatise. In it 

 too, though not to the same extent, for its aim is different 

 in some degree, there is a good deal of fairly advanced 

 theory, and like the former work, it shows no shirking 

 or glossing over of difficulties. It contains a more de- 

 tailed account of the experimental details of the subject 

 than the other work, and this, by the use of a somewhat 

 small but still perfectly clear type, is got in without un- 

 duly swelling the volume. The two books read together 

 would form an excellent combination. They are enough 

 to give any competent student a most desirable acquaint- 

 ance with the essential parts of the main phenomena, 

 and their elementary theory. Such a student would 

 afterwards go easily and rapidly forward with the study 

 of the more elaborate theoretical works, and of the re- 

 searches which have lately advanced electricity so much 

 — the absolute determinations of electrical constants 

 which have been made by so many experimenters, and 

 the improved science of electrical measurement which 

 these, together with the experimental investigation of the 

 electromagnetic theory of light, and the vast development 

 of practical electricity, have brought into existence. 



A. Gr.w. 

 NO. 1388, VOL 54] 



ANNALS OF THE CALCUTTA BOTANIC 

 GARDEN. 

 A>?na/s of ilie Royal Botanic Garden, Calcutta. Vol. v. 

 Part I. Pp. 9 +68, loi plates. (Calcutta : the Bengal 

 Secretariat Press, 1895. 



THE Royal Botanic Garden, Calcutta, has been pub- 

 lishing from time to time a series of "Annals," 

 illustrative of the flora of the continent of India, the 

 adjacent islands, and the contiguous countries. Volume v. 

 of this work was published last year, and Part i consists 

 of "A Century of Indian Orchids" by the chief of con- 

 temporary botanists, Sir Joseph Hooker. The Calcutta 

 Garden has had the advantage of the services and 

 labours of a long series of eminent botanists. Volume v. 

 of the " Annals " is dedicated to perhaps the most dis- 

 tinguished of them, Roxburgh, superintendent from 1793 

 to 1 8 14, and author of the " Plants of the Coromandel," 

 the " Hortus Bengalensis," and the "Flora Indica," of 

 whom a portrait and a brief memoir are prefixed. It 

 may be well to recall the names of Roxburgh's successors 

 to show how well botany has been served in connection 

 with these gardens. They have been Wallich, Falconer, 

 Thomson, Anderson, Clarke, and King ; the last named, 

 an admirable administrator and a distinguished botanist, 

 being still in charge. 



Since Roxburgh's time, that is for more than a century, 

 what Sir Joseph Hooker describes as a "magnificent 

 series of Indian plant-portraits by native artists " has 

 been accumulating in the Calcutta Botanic Garden, of 

 which about a thousand are those of orchids. 



" The most important of these collections," says Sir 

 Joseph ("Flora of British India," vol. v. p. 176) 

 " were Malayan, abounding in novelties from Penang, 

 Perak, Singapore and Malacca, made by the late Father 

 Scortechini, ... by Kunstler (a collector sent from the 

 Calcutta Botanical Gardens by Dr. King), by Curtis 

 Hullett, Wray and Ridley. Important collections w-ere 

 also sent by Mann from Assam, Bhotan, and the Khasia 

 Hills ; by Gamble from various parts of India ; by 

 Duthie from Garwhal ; by Clarke from -Sikkim, the 

 Khasia Hills, and Bengal, together with a ie.\\ from 

 Central India ; and by Dr. Trimen from Ceylon." 



So little accessible were these drawings, and so little 

 was their value known, that it was not until Sir Joseph 

 Hooker had almost completed, as he mentions in his 

 brief preface to the " Century," the descriptions of Indian 

 orchids for his monumental work, the "Flora of British 

 India," that he obtained, through Dr. King, the loan of 

 the native drawings referred to. .Sir Joseph further states 

 that "the inspection of these drawings," coupled with 

 the study of other material received from Calcutta, 

 "necessitated a revision of the characters of the greater 

 portion of the species already described, . . . together 

 with the addition of not a few new species." 



With reference to these drawings, the author states 

 that, excellent as they are in many respects, they betray 

 " that tendency to enlarge, which is the besetting sin of 

 Indian botanical artists." Perhaps it is rather the in- 

 difference to exact accuracy — a strongly-marked charac- 

 teristic of all Indian artists — which is in fault. No one 

 who has had to do with Indian workmen can have 

 failed to notice how difficult it is to induce them to re- 

 cognise the importance of accurate measurements and 

 proportions. 



