348 Prof. Knoblauch on the Connexion between the 



because the phcenomeiia by means of which it has to be measured 

 are of such a kind that their magnitudes have to be multiphed 

 and added in order to complete the measurement required, — just 

 as the volume of a body is a simple magnitude, although to 

 ascertain it we have to measure the three dimensions of each of 

 several parts into which we divide that volume, multiply them 

 together, and add the products. 



Momentum and angular momentum possess, like energy, the 

 property of conservation ; but they do not possess the propei'ty of 

 completeness, inasmuch as they take into account actual motions 

 only, and not tendencies to move. Attraction takes into account 

 tendencies to move only, and not actual motions. Energy alone 

 takes all those relations into account. 



The attempt to measure the " force," " energy," or " power " 

 of a system of gravitating bodies (by what term soever the 

 quantity to which the law of conservation of energy applies is 

 designated) by taking into account only the attractions, or ten- 

 dencies to mutual approach of the bodies, would be analogous to 

 the attempt to measure the volume of a body by means of one 

 dimension of one of its parts. 



It appears to me that the consideration of the facts T have 

 mentioned tends to show that there is less real difference between 

 the opinions of ])r. Faraday and those of some other writers on 

 this subject than may at first have been supposed. 



I wish it to be understood, that nothing in these remarks is 

 to be construed into an expression of any opinion on any meta- 

 physical question relative to the nature of physical causation. 

 I am, Gentlemen, 



Your most obedient Servant, 



Glasgow, April 13, 1859. W. J. Macquorn Rankine. 



LVI. On the Connexion between the Structure and the Physical 

 Properties of Wood. By Prof. Knoblauch*. 



THE author seeks to ascertain lohether any connexion is ascer- 

 tainable between the structural relations of various kinds of 

 wood and their observed physical properties, such as their poivers 

 of resonance and conduction of heat, ^-c, in the same way as was 

 done for one and the same wood by Savart in respect to resonance, 

 and more especiallyby Tyndall in respect to the conduction of heat. 

 The primary object was to trace the difference in the conduc- 

 tion of heat shown by difi"erent woods, according as the heat has 

 to traverse the wood in a direction parallel with, or at right 

 angles to, the direction of the grain. For this purpose, slabs of 

 the woods to be examined were bored through perpendicular to 



* Translated by Dr. F. Guthrie, from the Sitzungsberichte der natur- 

 forschenden Gesellschaft, Halle, 1858. vol. v. 



