464 



NA TURE 



[March 20, 1902 



Index Kewensis Plantarum Phancrogarum. Supplemen- 

 turn primtim. By Theophilus Durand et B. D.iydon 

 Jackson. Pp. 120. (Brussels). 

 On the title-page of this, the first supplement to the 

 " Index Kewensis," the name of Monsieur T. Durand, the 

 director of the botanical (garden at Brussels, is associated 

 with that of Mr. Daydon Jackson, the author of the original 

 work. Mr. Durand is mainly responsible for the new 

 part, which deals with species and varieties which have 

 been named during the decade 18S6-1S95. In order to 

 maintain uniformity, the same arrangement is adopted as 

 in the " Index Kewensis.'' Most of the new plants are 

 tropical, and quite an appreciable addition is due entirely 

 to Kuntze, who has upset several of the ordinarily ac- 

 cepted genera, though for the most part species names 

 are unchanged. This part takes the genera as far as 

 Cymbidium. 



It is hardly necessary to point out the importance of 

 keeping a standard work of this kind up to date, and the 

 author has rendered a great service to systematic botanists 

 in bringing out so quickly, considering the great labour 

 involved, this additional record of plant names. 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to 10? respond with the writers of, rejected 

 manuscripts intended for this or any other part of NATURE. 

 No notice is taken of anonvmons communications.'\ 



The Misuse of Coal. 



As England has taught the world how to use coal, she ought 

 to think of teaching the world how to use coal without waste. 

 Coal is so plentiful, so cheap ; it is so much to the interest of 

 many people that the waste should go on, and the general public, 

 who alone can apply a remedy, are so ignorant of natural science 

 that when, every few years, I draw attention to this subject, I 

 feel my efforts to be hopeless. Nevertheless, you will perhaps 

 allow me to call attention to the fact that in the very best and 

 largest steam-engines less than 10 per cent, of the energy of 

 coal is utilised ; in many small engines only i per cent. The 

 remaining energy is quite wasted. 



In the electric generating station of a city like Manchester, 

 there are engines of 12,000 horse-power, driving tram-cars and 

 house-lights. In a line of battle ship there is more than twice 

 this power. Two new Cunard steamers are, I understand, about 

 to be ordered, each of which will have 48,000 horse-power. 

 The great waste of energy inevitable in all heat engines of the 

 world is therefore enormous. 



It is known that when fuel energy is converted into the electric 

 form directly, as in a voltaic cell, more than 90 per cent, of the 

 fuel energy is convertible into the mechanical form, but at present 

 contrivances to do this even in the case of gaseous fuel are too 

 bulk)* and expensive to compete with heat engines. I wish once 

 more to suggest that an organised attempt be made to convert 

 the energy of coal into electric energy in some form of engine 

 which shall not cost more or have greater weight than a steam- 

 engine of the same power. 



For the heating of buildings. Lord Kelvin pointed out long 

 ago that the very law of thermodynamics which makes a heat- 

 power engine inefficient makes it possible to obtain from one 

 unit of energy the effect of 50 or 100 units by direct heating. I 

 know of nothing which so well illustrates the scriptural promise 

 of the seventy and seven fold reward of virtue as this. Discover 

 the energy engine and you multiply your power to heat buildings 

 from coal, seventy and seven times. But how can we make facts 

 of this kind obvious to ordinary men — the men who are said to 

 NO. 1690, VOL. 65] 



be educated when they know absolutely nothing of physical 

 science ? Even with coal as cheap as it is we might appeal to 

 its selfish users by pointing out that with the new kind of engine 

 a ship would be able to travel ten times as far at full speed as 

 she now can do without coaling. 



The world's yearly output of coal recently was 663 million 

 tons. Of this Britain's share was 30J per cent. If the whole 

 of the energy of Britain's coal for one year could be utilised 

 and charged for at 'id. per Board of Trade unit, the price paid 

 in many towns by consumers of electric energy, it would 

 amount to 100 times our national debt. It is to be remembered 

 that the cost of human labour when used most economically is 

 nine times the figure here given. 



Here is another fact. Scientific men know of no other store 

 of energy available for man's use than fuel from the earth, 

 except what we may get by the help of the tides or by wind or 

 waterfalls. To depend upon the future di scovery of some great 

 store is to act like a spendthrift who knows of no relation whose 

 death will give him more money and yet who goes on wasting 

 his substance. The energy of coal is the foundation of such 

 widespread comfort as we now observe all over the world. To 

 put the matter in a very definite form we may say : — the cost of 

 one Board of Trade unit of energy by the agency of human 

 labour working most economically is seventy pence ; the cost of 

 the unit as given out by a large steam-engine in a cotton factory 

 is one farthing ; the cost per unit of the coal alone (at 8.;. per 

 ton) if all its energy were utilised is one one-hundredth of a 

 penny. But when our coal supply is exhausted, when all the 

 races of the world have fought for the waterfalls and places of 

 high tide, the price must go back to the higher figure. The 

 failure of our coal supply is one of the two things neglected by 

 Mr. Wells in his " Anticipations," the recollection of which 

 would have modified all his conclusions. When coal becomes 

 scarce, people will wonder how it was possible for the nations 

 to spend so much money as they all now do, and our grass- 

 hopper weight of a national debt will seem to be an unbelievable 

 burden. Seventy pence to a farthing is the ratio of values 

 without and with coal even now, and the ratio ought to be ten 

 times as great, or 2800 to i. 



In sixty years we have greatly destroyed that store of energy 

 which is the foundation of what some of us call civilisation. 

 In another hundred years the English hamlets of conten ted 

 working folk that have become cities of luxurious people will decay 

 again into hamlets, inhabited by a discontented, poverty-stricken 

 population which will curse itsancestorsfortheir prodigality. They 

 will not curse us for using coal perhaps, but they will know 

 how to economise coal, and so they will curse us for our ignor- 

 ance. Over and over again have I called attention to the fact 

 that we are wasting the energy-capital of all the inhabitants of 

 the earth for all time to come. The value of human labour 

 gives the normal value of energy, and at this rate we in England 

 are wasting 900 times the amount of our national debt every 

 year. I have dragged this matter into my lectures and papers 

 with and without relevancy many times, and every one of my 

 hearers and readers neglects its significance. Scientific men 

 know it, but they think it useless to try to impress the ordinary 

 citizen, so ignorant of natural science as he is and so unheeding 

 of any kind of danger which was unknown to his forefathers. 

 What annoys me particularly is not so much the selling of my 

 birthright as that I should sell it for such a mere mess of 

 pottage. 



To return to my cry for a new invention. Many men have 

 advanced the subject beyond its first principles ; they know of 

 directions in which to work with prospects of success. In the 

 animal machine the thing is actually done ; but of this machine 



