Analysis of Scientific Books and Memoirs. 155 



that it was nearly equal to that of retardation arising from buoyancy, so 

 that in a brass pendulum (Spec. Grav. 8.8) with an arc of vibration of 3° 

 53' 10" and in a mercurial pendulum with an arc of vibration of 3° 3' 28", 

 the retardation from buoyancy is exactly compensated by the acceleration 

 arising from the reduction of the circular excess. 



Hence, if in every clock, the arc of vibration is so adjusted as to make 

 the retardation from buoyancy equal to the retardation caused by the cir- 

 cular excess, and if the density and consequent resistance of the medium 

 be supposed to change, the incremental variations of the times arising from 

 these two causes will be equal and in opposite directions. 



4-. Reverend Mr Lardner's method of securing Carriage Wheels on their 



Axles. 



This ingenious contrivance is represented in Plate I. Fig. 26, 27, 28. 

 In Fig. 26, AB is the part of the axletree on which the wheel revolves, 

 BC a stop or spud forming part of the axletree, and within which the 

 wheel revolves, and CD a screw having a perforation with a linch pin, as 

 shown in Fig. 28. 



The nave of the wheel is shown in Fig. 27, where may be seen the 

 groove m which receives the stop or spud BC. When the wheel is about to be 

 placed upon the axle, this groove must be brought opposite the spud BC, 

 Fig. 26, so as to pass over it. The wheel will then revolve within the spud, and 

 cannot come off the axletree, unless the groove m first pass over the stop BC, 

 during which process the wheel cannot revolve. A slide or wedge EF, 

 made to fit the groove exactly, is inserted when the groove is not opposite 

 the spud, so that the wheel cannot come off, unless this slide works out. 

 A collar GH, Fig. 28, with an aperture corresponding to the stop BC. 



Art. XXX.— ANALYSIS OF SCIENTIFIC BOOKS AND 

 MEMOIRS. 



I. Account of the Earthquakes which occurred in Sicily, in March 1823. 

 By Sig. Abate Ferrara, Professor of Natural Philosophy in the Uni- 

 versity of Catania. 



This curious Memoir, of which we intend to give an abstract, may be 

 divided into two parts, the first of which gives an account of the general 

 phenomena and effects of the earthquakes, and the second relates to the 

 physical explanation of the phenomena- 



On Wednesday, the 5th of March 1823, at 26m. after 5 p. m., Sicily suf- 

 fered a violent shock of an earthquake- The first shock was indistinct, but 

 tending from below upwards ; the second was undulatory, but more vigor- 

 ous, as though a new impulse had been added to the first, doubling its 

 force ; the third was less strong, but of the same nature ; a new exertion 

 of the force rendered the fourth equal on the whole to the second ; the 

 fifth, like the first, had an evident tendency upwards. Their duration was 



