332 



NATURE 



[August 5, 1897 



stresses on the connecting-rods were always those of com- 

 pression. With such an arrangement naturally a given cylinder 

 only does half the work that can be obtained from a double- 

 acting cylinder of the same capacity, and this leads to additional 

 weight and space being required for the single-acting engine. 

 For this reason it was the common practice, and still is to a 

 large extent, to run the necessarily quickly rotating dynamo 

 belt-gearing from a large engine making moderate revolutions, and 

 occupying much space ; but for a considerable time past the high- 

 speed, single-acting engine, coupled direct, has been a formidable 

 rival. The high-speed double-acting engine has also been growing 

 in favour of late, and, as has been stated, undoubtedly has ad- 

 vantages. The dynamo-electric machine has certainly done one 

 good thing — it has raised the standard of stationary engine design 

 and manufacture enormously, just as the torpedo boat did for 

 marine engineering. The chief features dealt with by Mr. Morcom 

 in his paper were lubrication and vibration, the two great 

 difficulties to be met in quick-turning engines. To eft'ectually 

 lubricate bearings a force-pump is employed, which continuously 

 injects oil at pressure into the space between the shaft or journal 

 and the bearing. The reciprocation of pressure of the shaft on 

 the bearing assists the circulation of the lubricant for the follow- 

 ing reason : when strain is above the piston, and the connecting 

 rod is in compression, the journal will be pressing on the bottom 

 brass — we put out of consideration any tendency of the shaft to 

 bend — and, as a journal can never be an absolutely tight fit in 

 its bearing, there will be a space between the top bearing and 

 the shaft. Into this space oil is at once forced by the pressure- 

 pump, and when the stress is reversed the film of oil remains 

 during the whole of the up-stroke, because there is not time to 

 squeeze it out from between the rubbing surfaces before the 

 pressure is again released. The same thing, of course, applies 

 to the bottom brass, and in this way there is always a liquid 

 film of oil between the journal or shaft and the brass 

 or bearing, and the two, therefore, never come in contact. 

 Observed data support the latter view, as the wear 

 on journals has been found to be inappreciable after 

 considerable running ; but perhaps the best testimony is 

 that Prof. Kennedy, in an exhaustive test of one of these 

 engines, found the mechanical efficiency of the machine to be 

 96 '3 per cent. It will be seen that in this matter of distributing 

 the oil on the bearing surfaces the double-acting engine has an 

 advantage over the single-acting engine, where the pressure is 

 always in one direction, and is never released while the engine 

 is running, although it may be relaxed. In regard to vibration 

 so much has been done lately, especially by the builders of 

 torpedo craft, that not much is left to add. It may be said 

 that Mr. Morcom is fully alive to the need for providing against 

 the disturbance "due to couples produced by the changing 

 momentum in the several lines of moving parts," and that 

 occasioned by the obliquity of movement of the connecting-rod. 

 He refers to Mr. Yarrow's admirable experiments, and considers 

 the effect of crank angle and multiple cylinders. We have not, 

 however, space to go into these problems, and must refer our 

 readers to the original paper. 



A long and interesting discussion followed the reading of the 

 paper. 



There were several excursions to neighbouring towns, where 

 works were visited, speeches made, and luncheons eaten after 

 the manner of meetings of this kind. One of the trips which 

 attracted a great deal of interest was that to Coventry, where 

 the much-discussed "motor-mills" where " horseless carriages " 

 are made in such profusion, according to certain glowing 

 accounts, were to be inspected. This establishment is said to 

 be "the largest and best organised for the purpose in the 

 country." To judge by what was seen in regard to work in 

 progress, there need not be much fear that the country will be 

 flooded by horseless carriages for some time to come yet. 



A TROUBLESOME AQUATIC PLANT. 

 ■pOR several years past an aquatic plant known as 

 ^ the water hyacinth has been developing to such an 

 enormous extent in the St, Johns River, Florida, as to cause 

 serious apprehension in that region regarding its possible 

 obstruction to navigation. About two years ago the War 

 Department was asked to investigate the matter, and did so. 

 In answer to urgent requests for exact information on the 

 subject, the Department of Agriculture, on January 25, directed 

 one of its agents, Mr. Herbert J. Webber, an assistant in the 



Division of Vegetable Physiology and Pathology, to visit 

 the region and prepare a report covering the following points : 

 (i) Historical notes regarding the plant, including its habitat, 

 manner of growth, propagation, and anatomical and physio- 

 logical characters ; (2) an account of its introduction and spread 

 in Florida ; (3) the present distribution of the plant in the 

 State, and its effect on navigation and commerce ; and (4) possi- 

 bilities of exterminating it. Mr. Webber's report has now been 

 issued from the Government Printing Office, Washington, and 

 is very exhaustive. The plant is mostly limited in its growth 

 to sluggish fresh-water streams, lakes, &c. , and the character of 

 the water appears to have much to do with its growth. It can 

 endure only a small percentage of salt, and is killed when it 

 floats down into the sea-water. It is normally propagated by 

 seeds and by stolons. Its introduction into the St. Johns River 

 look place about 1890, when a number of plants were thrown 

 into it. They grew there luxuriantly, producing beautiful masses 

 of flowers which rendered the river attractive. At this time 

 no one suspected that the plant would become a nuisance, and it 

 was introduced at various points to beautify the river. In a short 

 time it interfered very materially with navigation, making it, 

 in fact, both difficult and dangerous. Its effect has been most 

 disastrous to those engaged in the lumber trade and in the fish- 

 ing industry. It is feared that eradication is impracticable, 

 but suggestions are made as to possible methods for keeping the 

 evil in check. Of these the one most in favour with the author 

 is the use of a light-draught stern-wheel steamer, having a double 

 bow or outrigger, which, being forced into a mass of plants, 

 would cause them to gather towards the middle of the boat, 

 vvhere an inclined carrier would pick them up and deposit them 

 in front of rollers driven by machinery, which would force the 

 water from them, thus greatly reducing their bulk. The crushed 

 material could be delivered to barges alongside, to be deposited 

 where no injury could again result, or a cremator could be 

 arranged on a barge alongside of the boat, and so save additional 

 handling. 



NO. 1449, VOL. 56] 



THEORY AND PRACTICE} 

 T PROPOSE to speak to-day of the relative importance Oi 

 -'■ theory and of practice in the arts ; and especially, of course, 

 in the art of medicine. It is said that Englishmen are falling 

 behind other nations, and especially behind the German nation, 

 in their perception of the value of theory in the practical arts. 

 Now this is somewhat strange and inconceivable to us. English- 

 men proudly feel in this year of the Greater Jubilee that their 

 achievements in the conduct of life are not only great but incom- 

 parable. Not only has England become great as an empire, 

 as the Roman Empire ; it is great also in the achievements ot 

 the intellect : the land of Roger Bacon, of Francis Bacon, of 

 Newton and Adams, of Berkeley, Locke and Hume, of Boyle, 

 Priestley, Cavendish and Dalton, of Young and Faraday, ot 

 Harvey, Owen, and Darwin, need not be ashamed even before 

 the brilliant nation of Descartes and Laplace, of Lavoisier and 

 Cuvier, of Pare, Bichat, and Bernard. Nor will I forget to 

 speak of our place in letters, wherein we acknowledge none as 

 our masters ; for it is of the gifts of imagination no less than of 

 the gift of analysis that scientific theory is born. Can it be true, 

 then, that with these endowments we are to fall behind in the 

 practice of the arts because, as a nation, we have no due sense 

 of the bearing of theory upon practice ? 



It cannot be doubted, I fear, that, in some departments of 

 knowledge we are falling behind relatively if not absolutely ; 

 that we nave failed to keep before ourselves a due sense of the 

 value of theory, and have forgotten that, although in general- 

 isation we should never lose our hold upon detail, nor lose 

 our tact in converse with the manifold aspects of life, nor our 

 memory of the devices whereby we must meet the incursions 

 of contingencies often themselves incalculable, we shall never- 

 theless fall behind in the fight with reluctant nature if we 

 do not incessantly revise our formulas in the light of pro- 

 gressive research on more and more general lines. We have 

 perhaps forgotten that the work of Walt and Stephenson 

 would have made little progress but for the great modern 

 advances in thermodynamics in which, among others, are 



1 Abstract of an address delivered at the combined meeting of the Cam- 

 bridge and Huntingdon, the East Anglian, and the South Midland Branches 

 of the British Medical Association at Cambridge, by Prof. T. Clifford 

 AUbutt, F.R.S. Abridged from the British Medical Journal. 



