241 



was greater, or about 3*5, while the probable error was about the 

 same. By using a telescope with a cross view, as he appears to 

 have done lately, he has considerably reduced both quantities. But 

 each person should determine the amount of retardation for himself, 

 as depending upon his distance from the hill, peculiarity of ob- 

 servation, and other such causes. This done, and the quantity 

 applied to one of the rises as a correction, will give a very near 

 approximation to the error of the observer's watch, so that he will 

 be fully prepared to observe the instant of the drop to the utmost 

 exactness. 



8. Has the accuracy of the drop of the ball been independently 

 tested ? 



As to absolute time, not that I am aware of; but as to relative 

 time, it has by the two very careful series of observations already 

 mentioned, by Sir T. M. Brisbane and Mr Swan. The results of these 

 are given below in the rates of their chronometers, for similar days. 

 And it will be observed, that although one of them did alter its rate 

 somewhat irregularly backwards and forwards, still as the other was 

 going on in a uniform march at the selfsame time, the anomalous 

 effect was all owing to the one chronometer, and nothing sensible 

 was due to any error of the time-ball. 



In conclusion, the author observed that the arrangements which 

 were in the course of being made, would give uninterrupted facility 

 to tlie public for ascending to the top of the monument. 



3. On a Black Tertiary Deposit, containing the Exuviae of 



Diatomes, from Glen Shira. By Dr Gregory. 



4. Additional Note to a Paper on the Structure of Coal, and 



the Torbanehill Mineral. By Dr Bennett. 



5. On the Mechanical Energies of the Solar System. By 



Professor William Thomson. 



In this paper it is shown, that by the sun's heat there is an emis- 

 sion of mechanical energy from the solar system, amounting in 

 about 100 years to as much as the whole energy of the motions of 

 all the planets. The principal object of the paper is to investigate 

 the source from which this vast development of energy is drawn. It 

 is argued, that either a store of primitive heat must be drawn upon, 



