No. XII.] APPENDIX. 203 



standard, yet they would be able, for all practical purposes, to have ample 

 knowledge of our measures. All other measures would be obtained either 

 by multiplying the inch, or expressing the relation in fractional parts of 

 it." P. 34. 



Referring to the same point, he observes further on : 



"Our standard inch is no longer of the same length, and therefore not 

 an inch if the temperature varies ever so little from that point at which 

 the standard was assumed ; but let the temperature vary ever so much, the 

 number of particles cannot be multiplied or diminished, it is only the size 

 that varies. In conducting the ordnance survey of England, the measures 

 were obliged to be most carefully adjusted for temperature or variation in 

 the thermometer. So also in adjusting the standard bushel, the difficulty 

 was found to be extreme, for it was found that the heat caused by a human 

 body coming near so large a bulk caused a sensible alteration in its exact 

 size." P. 39. 



Having then spoken of the abstract ideas of length, breadth, cube, and 

 other geometrical properties of matter, he passes on to cohesion a state in 

 which a number of particles of the same kind of matter are attracted 

 together into a mass. 



" Bodies," he observes, " in a state of cohesion resist the action of 

 other bodies presented to them to an extent proportionate to that cohesion. 

 Lead, in an extremely divided state, burns vividly upon simple exposure to 

 atmospheric air, whilst the same metal in a state of cohesion, or in a rolled 

 malleable state, undergoes but little change from long exposure. Spongy 

 platinum, and other metals in a finely-divided state, also have very different 

 properties from the same metals in a state of cohesion. There is no more 

 curious instance of the effects of cohesion than in the varieties of coke ; 

 for when tinder, the slightest spark will inflame it; when soft coke, it 

 readily burns; when hard coke, it can scarcely be made to ignite; but 

 when a diamond, it requires a skilful chemist to inflame." P. 44. 



The threefold state in which bodies may exist solid, liquid, or 

 gaseous ; the various properties depending on the degree of attraction 

 such as hardness, softness, &c., are next spoken of in order ; and the author 

 having brought before our notice that attraction exerted between particles 

 of dissimilar matter known as chemical affinity, the remainder of the 

 chapter is occupied with the subjects of atomic weight, heterogeneous and 

 capillary adhesion, endosmosis, the attractions of gravitation and magne- 

 tism all of which topics are set forth in an equally novel, clear, and simple 

 manner. But we must hasten onwards from these to the third chapter, on 

 the sciences of the disturbance of attraction including electricity, mechanics, 

 hydrostatics, and pneumatics. 



"We have shown the mode in which attraction gives quality by 

 chemical affinity ; quantity, by the union of many atoms ; form, by the 

 mode in which the particles are united; size, by the intensity of the 

 attractive force ; and, lastly, position of masses by gravitation." P. 70. 



And we now have to see how these attractions may be disturbed or 

 destroyed by other attractions, acting in an opposite direction. 



In the study of the disturbance of attractions, he begins with con- 

 sidering the effects produced on a compound consisting of two elements, 

 when a third body is presented to it, which abstracts and combines with 

 one clement, setting the other free. 



