768 



SCIENCE. 



[N. S. Vol. VIII. No. 205. 



cases when the stop-valve is purposely used 

 for reducing the pressure. In such cases 

 the temperature of the steam at the reduced 

 pressure shall be substituted. In the case 

 of saturated steam the temperature corre- 

 sponding to the pressure can be taken. 



Lower limit : the temperature in the ex- 

 haust-pipe close to, but outside, the engine. 

 The temperature corresponding to the pres- 

 sure of the exhaust steam can be taken. 



(5) That a standard steam-engine of 

 comparison be adopted, and that it be the 

 ideal steam-engine working on the Eankine 

 cycle between the same temperature and 

 pressure limits as the actual engine to be 

 compared. 



(6) That the ratio between the thermal 

 efficiency of an actual engine and the ther- 

 mal efficiency of the corresponding standard 

 steam-engine of comparison be called the 

 efficiency ratio. 



(7) That it is desirable to state the ther- 

 mal economy of a steam-engine in terms of 

 the thermal units required per minute per 

 Indicated HP., and that, when possible, the 

 thermal units required per minute per Brake 

 HP. be also stated. 



(8) That, for scientific purposes, there be 

 also stated the thermal units required per 

 minute per HP. by the standard engine of 

 comparison, which can readily be obtained 

 from a diagram similar to that given, and 

 from which the efficiency ratio can be de- 

 duced. 



R. H. Thueston. 



IBE KINETIC THEORY OF GASES AND SOME 

 OF ITS CONSEQUENCES* 

 Though Science — Science with a capital 

 S — is often contrasted with Art — Art with 

 a capital A ; though the former is held to 

 be dry and unattractive, while the latter 

 stirs the imagination and arouses 'thoughts 

 that breathe and words that burn ;' yet the 



*Eeprinted from the Contemporary Review for No- 

 vember, 1898. 



follower of science now and then is re- 

 warded for his toil by an ordered sequence 

 which appeals to the imagiuative side of his 

 nature, no less than the rhythmic harmony 

 of poetry, or the measured cadences of 

 music. Indeed, it is not impossible for the 

 poet to express better than, and as truly as 

 in the pages of the Philosophical Transactions, 

 the highest generalizations of science. In 

 this Tennyson stands unrivalled. Take, 

 for example, the stanzas : 



" There rolls the deep where grew the tree, 

 O earth, what changes hast thou seen ! 

 There where the long street roars, hath been 

 The stillness of the central sea. 



" The hills are shadows, and they flow 



From form to form, and nothing stands ; 

 They melt like mist, the solid lands. 

 Like clouds they shape themselves and go." 



It contains an epitome of the whole of 

 geology. The science is mere elaboration 

 of the ideas contained in Tennyson's beau- 

 tiful verses. 



The difficulty in gaining the appreciation 

 of the ' general public ' is in presenting the 

 ideas in intelligible language. That the 

 scientific and the romantic are sometimes 

 closely intermingled is indisputable ; but 

 the romance is one which appeals to few. 

 In the following pages an attempt will be 

 made to show how the thoughts of many 

 men, each striving to ' increase natural 

 knowledge,' as the formula of admission to 

 the Eoyal Society runs, have led to a dis- 

 covery of some interest — that of a hitherto 

 unsuspected constituent of atmospheric air. 



The Roman poet Lucretius, a friend and 

 contemporary of Cicero, was the author of 

 a poem entitled ' De Rerum ISTatura ' (' On 

 the Nature of Things'). In this poem, 

 which treats of almost all things in heaven 

 and earth, he argues that the atoms, the 

 existence of which is obvious because one 

 sees them in a coue of light passing through 

 a dark room, fall rapidly together in their 

 dancing course throughout the spheres. 



