NATURE 



[November 3, 1910 



who had no previous knowledge of it would be be- 

 wildered. No pure mathematician could be more 

 careless as to what the equations which he desires to 

 write down are based upon, or show less interest in 

 the question whether the results to which they lead 

 are verified. Moreover, he does not explicitly refer 

 to the base, relative to which the motions studied are 

 reckoned, according to the theory which he is using, 

 or appear to take any interest in the remarkable fact 

 that the observed motions of bodies define such a 

 base, which presumably has some relation to other 

 physical phenomena. The only occasion on which he 

 attempts to deal with the foundations of the subject 

 is in connection with the law of action and reaction 

 in statics, the treatment of which is clumsy and un- 

 convincing-, perhaps even unintelligible. 



As in tne case of the rest of physics, there are two 

 ways of looking at mechanics, each of which has its 

 own proper place. One is to regard all parts of the 

 subject as coordinated by means of a generalisation 

 which is as comprehensive as possible. The 

 other is to aim rather at isolating the points 

 involved in the subject, so that any degree of inde- 

 pendence which they possess may be recognised, and 

 so that it may as much as possible be seen how far 

 the most precisely ascertained results carry us, and 

 whether a doubt cast on any particular doctrine 

 affects the whole foundation of the subject or 

 not. Though the attainment of the former is the 

 constant aim of scientific study, the latter is the 

 proper attitude in which to approach it, and it seems 

 to be a mistake to write the first chapter of physics in 

 a different spirit. W. H. M, 



CANNIZZARO'S COURSE OF CHEMICAL 

 PHILOSOPHY. 



Sketch of a Course of Chemical Philosophy. By 

 Stanislao Cannizzaro (1858). Alembic Club re- 

 prints. No. 18. Pp. iv + 55. (Edinburgh: The 

 Alembic Club, 19 10.) 



Tp"HE Alembic Club have done well at this juncture 

 J- to publish a translation of Cannizzaro's famous 

 letter to De Luca — a letter which, to use Davy's 

 phrase in connection with an equally memorable pro- 

 nouncement, acted like an alarm-bell on Europe. In- 

 deed, now that he has joined the majority, no more 

 fitting monument to the perspicacity and genius of 

 the great Italian chemist could be conceived than the 

 publication, in the form of an admirably executed 

 translation, of that statement of doctrine which 

 astonished and ultimately convinced the chemical 

 world of the mid-Victorian epoch. 



To the chemists of the present age it is hardly 

 possible to convey an idea of the profound sensation 

 which this letter created. The effect was immediate 

 and irresistible. At that time the name of Canniz- 

 zaro was hardlv known beyond a limited circle of 

 French and Italian men of science. With the appear- 

 ance of the message came the conviction that a 

 Daniel had come to judgment — that a prophet and a 

 law-giver had arisen amongst us. The middle period 

 of the last century was a time of political ferment 

 NO. 2140, VOL. 85] 



and social unrest, and here and there it culminated ii 

 revolution. It was equally a period of disturbanci 

 and upset in other spheres of human activity than 

 politics and sociology. In chemistry, more perhaps 

 than in the case of any other science at that time, the 

 old order was changing, but the process was destruc- 

 tive rather than constructive. Old faiths were being 

 undermined and thrown down, but the new dogmas 

 had not stability enough to supplant them. 



Cannizzaro's letter appeared at what, in the cant- 

 phrase, is termed the psychological moment. It 

 brought order, method, and arrangement into what 

 hitherto had been a mass of inconsistency and con- 

 tradiction. Its logic was so clear, its appeal to history 

 and to well-ascertained fact so irrefutable, its state- 

 ment of proof so admirably marshalled, that criticism 

 was silenced, and the doubter disarmed. Before a 

 decade had passed its principles were everywhere 

 accepted, and it is not too much to say that Canniz- 

 zaro_ effected a revolution in chemical thought as 

 momentous in its way as the revolution he was sub- 

 sequently concerned in bringing about in the political 

 development of Italy. 



To the student of chemistry it would be superfluous 

 to enter into an analysis of Cannizzaro's letter, as 

 its principles are now intimately woven into the web 

 of modern chemical doctrine. Indeed, so indissolubly 

 associated is the fundamental basis of Cannizzaro's 

 chemical philosophy with the chemical philosophy of 

 to-day that the statement of these principles, or of 

 the course of argument upon which they are based, 

 would have the semblance of a platitude. But we can 

 assure the student that, however familiar he may be 

 with the outcome of the doctrine with which the name 

 of Cannizzaro will be imperishably connected, he will 

 read with admiration and delight the pronunciamento 

 in which the Genoese chemist makes known to his 

 friend and colleague, and through him to the world, 

 the dogma of what was henceforth to be the new- 

 chemistry — with admiration for the extraordinary per- 

 spicacity and conviction of its argument, and with 

 delight at the simplicity and force of its statement. 



T. 



PRUNING OF FRUIT TREES. 



Fruit Tree Pruning. A Practical Text-book for Fruit- 

 growers working under the Climatic and Econoinic 

 Conditions prevailing in Temperate Australia. By 

 George Quinn. Pp. vi + 230. (Adelaide, Australia: 

 R. E. E. Rogers, Acting Government Printer, 1910.) 

 Price IS. 3d. 



THE pruning of fruit trees is an operation that de- 

 mands, on the part of the operator, first, an inti- 

 mate knowledge of the natural habits of the particular 

 trees, and, in the second place, considerable experience 

 of the general results which follow a proper system 

 of pruning. Unfortunately, every gardener and 

 amateur who cultivates ever so few trees gets the 

 conviction that, come what will, he must prune, and, if 

 he is ignorant of the methods, nevertheless he 

 mutilates the branches and imagines that his trees 

 will respond satisfactorily to the treatment given 



J 



