July 



I. 



igoQl 



NA rURE 



a clear idea of the composition of forces, at a time 

 when the fundamental principles of dynamics were 

 unknown. 



The writings of the German philosopher Nicolaus 

 de Cusa seem to have made a profound impression on 

 Leonardo, and M. Duhem shows how suggestive they 

 were to him in his studies on the motion of bodies. 

 Leonardo discussed the motion of an arrow shot ver- 

 ticallv upwards from the earth, assuming the latter to 

 rotate in twenty-four hours, not because he wanted 

 to prove or disprove the rotation of the earth, but 

 merely as a problem of dynamics. Here, as well as 

 in his general investigation of the motion of a pro- 

 jectile, he found it hard to free himself from old ideas ; 

 he believed, for instance, that a cannon ball at first 

 moves in a straight line while influenced by a " violent 

 force," next in a curved path while that force and 

 gravity are struggling for supremacy, until it finally 

 drops to the earth in a straight line. Though he 

 cannot be considered a precursor of Copernicus (he 

 says repeatedly that the earth is at the centre of the 

 universe), he reasons as freely as Cusa about the 

 nature of the stars, and rejects the Aristotelean dis- 

 tinction between the terrestrial elements and celestial 

 uiatter. He believed the moon to be composed of the 

 four elements which it supports in space in itself and 

 by itself, as the earth does with its component parts. 

 This is much the same as the statement of Copernicus 

 that gravity is a natural tendency of all particles to 

 join themselves into a whole in the form of a sphere, 

 a tendency which is innate in the sun, moon, and 

 planets. 



The fourth essay deals with speculations on the 

 origin of fossils. Leonardo did not consider them to 

 be " plays of nature," or to have been carried to the 

 tops of mountains by a deluge, but recognised that 

 they are the remains of animals which actually lived 

 on the spot where the fossils are found. 



P.IAM RUBBER. 



(Icvi-ci bnisiliciisis, or Para Rubber. Its Botaiiv, 



Cultivation, Chemistry, and Diseases. By Herbert 



Wright. Third edition. Pp. xviii + 204. (Colombo : 



A. .M. and J. Ferguson ; London : MacLaren and 



Sons, iqoS.) Price lox. net. 



A REVIEW of Mr. Herbert Wright's valuable 



*• work on Para rubber appeared in Nature 



about two years ago. The present edition (third) has 



b^en considerably enlarged, and in Mr. Wright's 



words " has been compiled in consequence of the 



many advances which have been recentlv made in 



methods of cultivation and tapping, coagulating and 



curing." The text has been increased from 177 pages 



to 304 pages, and the really well reproduced and 



instructive illustrations from 86 to 272. Many of the 



chapters hav-e been re-written and expanded, especially 



tlie one on uses of rubber. There is now a 



separate chapter on the botany of the Para tree, Hevea 



brasiliensis, and one on the effect of tapping on the 



trees. 



Chapter iv. contains a great deal of useful and 

 NO. 2070, VOL. 81] 



up-to-date information on planting operations and on 

 catch crops. The advantages and disadvantages of 

 close planting are fully considered. The most general 

 distance now employed is from 15 feet to 20 feet. 

 The main justification for close planting is the in- 

 creased tapping area which is available in the first 

 few years, but there is a note of warning in the 

 following passage : — 



" No one who has seen the uncultivated thirty- 

 year-old trees at Henaratgoda can doubt that such 

 specimens require at the very least a distance of 

 tliirty to forty feet if they are to be allowed to con- 

 tinue in their growtli and maintain a healthy con- 

 stitution." 



Catch crops, says Mr. Wright, are all very ex- 

 hausting', and their profitable cultivation is limited to 

 about the first four years. 



Considerable space is devoted to a description of 

 the various methods of tapping and tapping imple- 

 ments, but, apparently, the systems employed are 

 far from perfect, as the following passage implies : — 



" The adoption of better systems of tapping which 

 obviate the necessity of paring away the tissues 

 wherein the milk accumulates, and drawing supplies 

 of latex by merely cutting and not excising the lati- 

 ciferous tissues is bound to result in an increased 

 yield since the life of the tapping area is so much 

 prolonged." 



At present the average yield per tree per year 

 for the Malay States would appear to be about 2 lb. 

 Most of the trees, however, are still young. The 

 cost of production is about is. 6d. per lb. Various 

 methods of coagulating and treating latex are de- 

 scribed : the use of centrifugal machines is more or 

 less experimental; "the principle .... of causing 

 a separation of the caoutchouc globules by mechanical 

 means is one which cannot be too strongly impressed 

 on the experimentalist." 



There is very little doubt, from Mr. Wright's 

 remarks and his inquiries amongst manufacturers, 

 that plantation Para is inferior in quality to fine 

 hard (wild) Para. A wise manufacturer would not 

 dare to buy 50 tons of cultivated rubber and store for 

 six months, for fear of grave deterioration in quality, 

 but he would buy thousands of tons of up-river fine 

 Para with a full knowledge that it would grow better 

 in storage. Mr. Wright appears to have very little 

 faith in the so-called " synthetic rubber." 



Natural rubber consists chemically of very com- 

 plicated compounds. The " resins " and " proteins ■"•■ 

 are in themselves highly complex bodies, the com- 

 ponents of which are but little understood. 



" How can it then be possible, since we do not 

 fullv understand the chemical composition of the 

 various components of natural rubber, to have syn- 

 thetic rubber already on the market? " 



Mr. Wright's book is perhaps the most compre- 

 hensive and up-to-date work on Para rubber pub- 

 lished in this country, and has proved of great utility 

 to practical men in the various branches of the rubber 

 industrv. L. C. B. 



