FOR THE ADVANCEMENT OF SCIENCE. 119 



ther a level line agrees with low water, mean water, or high water, 

 and thus what is the true level of the sea. 



A paper was then read, by Mr. Lubbock, on the importance of 

 forming new empirical tables for finding the moon's place. 



Mr. Phillips next proceeded to offer a brief statement of the 

 means taken by the committee of the Association for the purpose of 

 procuring regular and uniform experiments on subterranean tempe- 

 rature. The errors incidental to observations made in the air or 

 water of mines had induced the committee to recommend observers 

 to attend simply to the temperature of the rocks themselves ; with 

 this view thirty-six thermometers had been duly compared, and the 

 errors of them ascertained. The results confirm the alleged increase 

 of temperature beneath the surface. In one instance the instrument 

 stood at seventy-eight degrees constantly, whilst the mean tempera- 

 ture of the air above was forty-seven degrees. 



Mr. Craig read a paper on Polarization, with a view to shew 

 that the phenomena are referable to the division, and consequently 

 to the weakening, of the impulse of light ; and the inability, there- 

 fore, to pass through other regular structures without exhibiting 

 phenomena which arise out of the peculiarities of such structures. 



Tuesday. — Professor Whewell having taken the chair, Mr. 

 Russell proceeded to read his paper on the practical applications of 

 certain principles of hydrodynamics, which had been developed in 

 the course of a series of experimental researches, in which he had 

 been engaged for several years. 



The investigations of Mr. Russell led to important results ; and 

 the present paper regards principles which open a wide field for the 

 improvement of the construction and transport on canals, and of the 

 navigation of shallow rivers. 



The increased resistance of a fluid to a solid moving upon its sur- 

 face, is well known, and has been supposed to follow the Newtonian 

 law. This is sometimes true, although very rarely. It is scarcely 

 ever true of a vessel moving in shallow water. For example, these 

 are resistances, measured in pounds weight, required to move the 

 same vessel at different velocities. 



Velocities in Miles an Hour. Resistance in Pounds. 



4 39 



6 91 



1\ 265 



81 215 



94 235 



12 352 



15 444 



These apparent inconsistencies had been reconciled with theory by 

 the discovery of a very beautiful phenomenon forming a most import- 

 ant element of the resistance. The law, connecting the resistance 

 with the velocity of the propogation of waves in the fluid, gave to 

 these results of experiment, unity and consistency. It had been ob- 



