Royal Society/. 131 



corresponding pole of a magnet. He then proceeds to the detail of 

 experiments for investigating the above-mentioned laws ; and to 

 their comparison with the results deduced from theory. These ex- 

 periments appear to him to establish beyond all doubt the influence 

 which the length of a needle has on its deviations produced by the 

 attraction of the shell of iron. When examined by the test of the 

 formulae given by the author, the law of the tangent of the deviation 

 being proportional to the rectangle of the cosine of the longitude into 

 the sine of the double latitude, on which so much dependence had 

 been placed, is found to give results so inconsistent with one an- 

 other, that it cannot be considered as even affording an approximation 

 to the truth, and must therefore be wholly rejected. 



The close agreement which the author found between the ob- 

 served and the computed deviations of needles whose magnetism had 

 been disturbed by contact with a magnet, as well as those which had 

 suffered no disturbance, fully confirmed him in the views which he 

 originally took of the action of iron on magnetized needles. He 

 conceives that his hypothesis, instead of being at variance with ob- 

 servation, is not only consistent with all the experiments that have 

 been made, but by affording the proper corrections to be applied to 

 them, derives the strongest support from these observations. 



He concludes by mentioning a fact which he conceives to be ir- 

 reconcileable with the hypothesis of induced magnetism j namely, that 

 a steel bar rendered as' hard as it was possible to make it, produced, 

 when its ends were reversed, precisely the same effect on the needle 

 as a bar of the softest iron under similar circumstances. 



June 12. — "An account of a series of experiments on the friction 

 and resistance of fluid and solid bodies retarded by the attrition of 

 their surfaces when rubbing against each other," by George Rennie, 

 Esq. F.R.S. 



The first part of this paper is occupied by a rapid review of the la- 

 bours of mechanicians on the subject of friction, from the period of 

 those of Amontons, at the end of the 17th century, to those of Cou- 

 lomb and of Vince, in the years 1779 and 1784 ; from which the au- 

 thor draws the conclusion, that the progress of knowledge in this de- 

 partment of science has been slow and unsatisfactory ; and that a 

 wide field is still left open to experimental investigation. With a 

 view to elucidate several points not yet sufficiently ascertained by 

 former writers, the author instituted several sets of experiments j 

 some calculated to determine the forces required for dragging bodies 

 of various kinds along a horizontal surface, and others for measuring 

 the angle at which a ])lane was required to be inclined to the horizon, 

 in order to admit of the body sliding down it : attention being paid 

 to the circumstances of pressure, extent of surface, time of previous 

 contact, and velocity of motion. 



The following are the principal conclusions which the author de- 

 duces from his experiment : 



The friction of ice rubbing upon ice diminishes with an increase of 



weight, but without observing anv regular law of increase. When 



dry leather was made to move along a plate of cast-iron, the resistance 



S 2 is 



