254 



NA TURE 



\yan. 12, I 



this is a subject which needs a chapter to itself, I may 

 pass on to more general remarks on what we have learnt 

 so far. 



It will be noticed that, whereas such fungi as Trametes 

 radiciperda and Agariciis melleus axq true parasites which 

 can attack the living roots of trees, the other fungi re- 

 ferred to can only reach the interior of the timber from 

 the exposed surfaces of wounds. It has been pointed out 

 along what lines the special treatment of the former dis- 

 eases must be followed, and it only remains to say of the 

 latter : take care of the cortex and cambium of the tree, 

 and the timber will take care of itself It is unquestion- 

 ably true that the diseases due to wound- parasites can be 

 avoided if no open wounds are allowed to exist. Many a 

 fine oak and beech perishes before its time, or its 

 timber becomes diseased and a high wind blows the 

 tree down, because the spores of one of these fungi 

 alight on the cut or torn surface of a pruned or 

 broken branch. Of course it is not always possible to 

 carry out the surgical operations, so to speak, which are 

 necessary to protect a tree which has lost a limb, and in 

 other cases no doubt those responsible have to discuss 

 whether it costs more to perform the operations on a large 

 scale than to risk the timber. With these matters I have 

 nothing to do here, but the fact remains that by properly 

 closing over open wounds, and allowing the surrounding 

 cambium to cover them up, as it will naturally do, the 

 term of life of many a valuable tree can be prolonged, 

 and its timber not only prevented from becoming diseased 

 and deteriorating, but actually increased in value. 



There is no need probably for me to repeat that, although 

 the present essay deals with certain diseases of timber due 

 to fungi, tliere are other diseases brought about entirely 

 by inorganic agencies. Some of these were touched upon 

 in the last article, and I have already put before the 

 readers of Nature some remarks as to how tree; and 

 their timber may suffer from the roots being in an 

 unsuitable medium. 



In the next paper it is proposed to deal with the so- 

 called " dry-rot" in timber which has been felled and cut 

 up — a disease which has produced much distress at 

 various times and in various countries. 



H. Marshall Ward. 



{To be continued.) 



PERPETUAL MOTIONS 



T F we study the past in order to trace the development 

 ■*■ of machines, we cannot help being astonished at the 

 long centuries during which man was content to employ 

 only his own muscular effort and that of animals, instead 

 of utilizing the other forces of Nature to do his work ; for 

 it is a striking fact that it is during little more than the 

 last quarter of a century that the power of the steam- 

 engine has in the aggregate become twice as great as that 

 of the whole working population of the world. 



Although the early history of the subject is shrouded 

 in obscurity, there is little doubt that the power of 

 water was the first to be employed. We can easily 

 imagine that, in those early days when the laws of 

 Nature were so little understood, the idea would arise 

 that, if some machine could be contrived which would 

 not get tired like man or animal, as machines appeared 

 to do when left to themselves, and, moreover, one which 

 did not depend upon a capricious and variable supply 

 of water, such a machine would go on for ever — in 

 short, would have perpetual motion. As a matter of 

 fact, Geiger. the German philologist, has adduced strong 

 grounds for believing the Buddhist praying-wheels — on 

 which the prayers of the worshippers were fastened, and 



Abstract of a Lecture d-ilivered by Pr f. Hele .Shaw, University College, 

 on December 2 1, 1887, in St. George's Hall, Liverpool. 



which were turned by water power — to be probably the 

 first kind of water motor : and at the same time the 

 first record of a proposal for a perpetual motion machine 

 appears to be in the " Siddhanta Ciromani," a Sanskrit 

 t;xt-book on astronomy, in which a wheel for this pur- 

 pose is suggested, having a number of closed equidistant 

 holes half filled with mercury upon a zigzag line round 

 its rim. No doubt other suggestions of this kind were 

 made from time to time, but writers and literary men 

 did not condescend to notice them, or even the progress 

 of the really practical and useful machines. We are thus 

 brought from that distant date down to the thirteenth 

 century, when we find in the sketch-book of an architect, 

 Wilars de Honecort (the original being now in the Ecole 

 des Chartres, at Paris), a drawingof a proposed perpetual 

 motion machine, with the statement which, translated, 

 runs : — " Many a time have skilful workmen tried to con- 

 trive a wheel that shall turn of itself: here is a way to 

 make such by means of an uneven number of mallets or 

 by quicksilver." The engraving shows four majlets upon 

 what is evidently meant to be the descending side of the 

 wheel, and three upon the ascending side, the former 

 therefore overbalancing the latter. To get the mallets 

 into this desirable position the top one on the descending 

 side has evidently been made to fall over before its time ; 

 but independently of this there is to the ordinary mind a 

 strong suggestion of speedy dissolution in any structure 

 a greater number of whose parts are going in one direc- 

 tion than in the other, but this little difficulty M. de 

 Honecort does not allude to or discuss. The unevenly 

 weighted wheel in which the action of gravity is to be 

 cheated in some way or the other has appeared in a great 

 variety of forms since, and, from the words "many a 

 time," probably before, and is by far the most important 

 type of proposed contrivance for perpetual motion. 



About two centuries after De Honecort, the famous 

 Leonardi da Vinci gives sketches of six designs, either 

 due to his own fertile brain or taken from other sources, 

 and since then there has been an incessant flow of pro- 

 posals of this type of machine, a large number of which 

 are given in the work of Dr. Henry Dirks, " Perpetuum 

 Mobile," and several in vol. xii. of the Mechanical 

 World 

 The next class of proposed machines we may consider 

 I are those in which gravity was to be made use of in one 

 I direction and evaded in the opposite, by the agency of 

 I falling water, amongst these being the devices of Schott, 

 j Scheiner, Bockler, and others. The idea in all these 

 was that a quantity of water might be kept circulating 

 between two tanks, one above, and one below ; being 

 raised to the upper one by means of pumps driven by a 

 water-wheel which derived its motion from the selfsame 

 water in falling the same distance, there being a balance 

 to the good in the form of extra work to be done by the 

 wheel. 



A third class of proposals suggests the application of 

 capillary action to raise the water instead of employing 

 pumps, one of the earliest being that of a Professor of 

 of Philosophy in Gla5gow about 200 years ag:o. In this 

 case and others the drawings show (in anticipation) the 

 water thus raised flowing out at the top in a good sub- 

 stantial stream, as, for instance, in the scheme of Branca 

 about the date of the Professor's production. 



The fourth and last class, which partook more of a 

 philosophic nature, proposed to employ magnets, the 

 attraction of which is to be eff'e;tive in one position, and 

 masked in another. There are many proposed ways of 

 effecting this, all equally futile, although one contrived by 

 a shoemaker of Linlithgow actually deceived for a time 

 Sir David Brewster, who communicated an account of it 

 to the Annales de Chimie: In the simplest a ball is to fall 

 through a certain distance, so as to come into a posi- 

 tion where it can be raised up an inclined plane by mag- 

 netic attraction. The first part is carried out in strict 



