368 Scientific Intelligence. 



Almost all the attempts which have hitherto been made for discovering 

 the laws of the resistance of fluids, are contrary to the first rule of experi- 

 ments, by which we ought to endeavour to decompose the phenomena into 

 their most simple elements. It has been most common, indeed, to observe 

 the time employed by different bodies, in describing a given space in a 

 fluid at rest, or the weight which keeps in equilibrium a body exposed 

 to the impulse of a fluid in motion. But this can only make us acquaint- 

 ed with the total result of the different actions, which this fluid exerts 

 upon each of the points of the bodies, actions which are very varied, and 

 often opposite to each other. In this state of things, compensations take 

 place, which mask the primitive laws of the phenomenon, and which 

 render the results of experiment inapplicable to any other case but that 

 which has furnished them. M. Dubuat, author of the Principes d'Hyd- 

 raulique, appears to have been the first who perceived this defect ; and, in 

 order to avoid it, he endeavoured to measure the local pressures on the 

 different parts of the surface of bodies, exposed to the impulse of a fluid 

 in motion. His experiments, though small in number, and though not 

 much varied, in so far as the form of the body is concerned, present, 

 nevertheless, curious results. Under these circumstances, the Academy 

 thought it would be useful to resume these experiments, with more per- 

 fect instruments, to multiply them, and to vary the circumstances still 

 more. It has proposed, therefore, for the subject of the prize, the follow- 

 ing programme : 



" To examine in its details the phenomenon of the resistance of water, 

 by determining with care, by exact experiments, the pressures separately 

 sustained by a great number of points, properly chosen in the interior, 

 lateral, and posterior surfaces of a body, when it is exposed to the impulse 

 of a fluid in motion, and when it moves in the same fluid at rest ; to 

 measure the velocity of the water -in different points of the current near 

 the body ; to construct from the results and observations, the curves which 

 these currents form ; to determine the point where their direction com- 

 mences before the body ; and, finally, to establish, if possible, from the ex- 

 perimental results, empirical formulae, which might be afterwards com- 

 pared with the experiments formerly made on the same subject." 



15. Dr Hare's Ijitrameterjbr ?neasuring Specific Gravities. — The object 

 of this instrument is to measure the specific gravities of fluids, on the prin- 

 ciple that, when columns of different liquids are raised by the same pres- 

 sure, their gravity must be inversely as their height. Two barometer 

 tubes, communicating with each other above, where there is a syringe to 

 withdraw the air, their lower ends rest in two cups, containing the two 

 fluids to be compared. The pressures upon the upper surfaces being then 

 removed by the syringe, the fluids rise in each tube to heights which 

 afford a measure of their specific gravities. — See Franklin's Journal, vol. i. 

 p. 157. 



MAGNETISM. 



16. Magnetic Declination at Byivell, in Northumberland, in 1824. — 

 Lieutenant Johnson has found the magnetic declination at this place, 





