68 Analyses of Books. [July, 



An Account of the Experiments to determine the Acceleration of 

 the Pendulum in different Latitudes. 



The nature of these experiments may be briefly described to 

 consist in ascertaining with the utmost possible accuracy at differ- 

 ent stations, the latitudes of which are correctly known, the num- 

 ber of vibrations which would be made by a certain pendulum in 

 a given time, were it placed at the level of the sea, in vacuo, and 

 at a certain temperature. This purpose is effected by setting up 

 a clock containing the pendulum in a convenient and protected 

 situation, and by observing the number of vibrations which it 

 makes on an average of several intervals of 24 hours each, accu- 

 rately determined ; the actual circumstances of the temperature, 

 pressure of the atmosphere, arcs in which the vibrations are 

 performed, and the elevation above the sea, being carefully 

 noted, and their effects in retarding or accelerating the vibrations 

 calculated and allowed for. This operation, which is sufficiently 

 simple in description, proves less so in the performance, by rea- 

 son of the extreme accuracy which is required in the results, 

 and of the many causes whereby slight errors may be intro- 

 duced, which demand the utmost precaution and watchfulness 

 to guard against. 



The squares of the number of vibrations in 24 hours in the 

 different latitudes are to each other as the force of gravitation in 

 such latitudes ; and the difference between the polar and equa- 

 torial diameters is deduced from the acceleration obtained by 

 comparing the observations at each station successively with 

 those at all the others. 



Two clocks were used in these experiments, being the pro- 

 perty of the Royal Society, and the same which accompanied 

 Capt. Cook round the world. The pendulums were prepared by 

 Capt. Kater, being each cast in one piece of solid brass, and 

 vibrating on a knife-edge of hard steel, on agate plates ground 

 into portions of hollow cylinders. 



The experiments were made in the present voyage, and in the 

 preceding one in 1818 ; one only of the clocks was employed 

 on the first voyage, but both in the second. 



The stations at which the experiments in 1818 were made 

 are as follow : 



At Brassa, one of the Shetland Islands, lat. 60° 09' 42" 0'" N. 

 At Hare, or Waysat Island, inDavis'sStrait, lat. 70 26 15 N. 

 At London, lat 5131 08 4 N. 



The stations of the present voyage were : 



In London, latitude as before. 



At Melville Island, in the Polar Sea, lat. ... 74 47 14 36 N. 



And again in London on the return of the expedition. 



The observations of the second voyage are deserving of prin- 

 cipal consideration for the following reasons : 



