Notices respecting New Books. 301 



tions of the masses before those portions themselves come close 

 up to the colliding surfaces. Now the pressure due to the sudden 

 condensation produced by the collision cannot transmit itself 

 with a greater velocity than that with which sound would travel 

 through the gases. Hence, if the masses collide with a velocity 

 much greater than that with which they would transmit sound, 

 the internal portions of the masses would not be brought gra- 

 dually to rest, but would move on with undiminished velocity 

 until they were brought to a violent check by meeting with a 

 partition of gases in an exceedingly condensed state. The sud- 

 den condensation thus produced, together with the heat evolved, 

 would put the gases into a condition highly favourable to che- 

 mical union. 



Now in the formation of nebulae I think that the velocity of 

 the colliding masses would be very much greater than the velo- 

 city of sound, and therefore that the above-mentioned effects 

 would be actually produced. Suppose, for example, that each 

 of the masses of gas contained as much matter as the sun, and 

 that their relative velocity was simply that due to their mutual 

 gravitation from a great distance : their relative velocity when 

 their centres of gravity were at a distance equal to the earth's 

 distance from the sun would be twice the orbital velocity of the 

 earth, or 36 miles per second, a velocity very much greater than 

 the velocity of sound in any gas whatever. 



A. S. Davis. 



Roundhay Vicarage, 



September 13, 1870. 



XXXVIII. Notices respecting New Books. 



Researches on Diamagnetism and Magnecrystallic Action, including the 

 question of Diamagnetic Polarity. By John Tyndall, LL.D., 

 F.R.S. London, 1870. 



TN this volume are reprinted Professor TyndalFs researches into 

 -*- the subjects mentioned in the title, together with abstracts of 

 lectures on these or kindred subjects delivered by him in the Royal 

 Institution, and several letters, essays, and reviews relating to similar 

 topics. In connexion with his own investigations into Diamagnetic 

 Polarity, Professor Tyndall has printed some extracts from papers 

 and letters by Faraday, Sir William Thomson, and Weber, in order 

 to make the theoretical discussion of the question more complete. 

 The papers here collected date from 1850 and subsequent years. 



As nearly the whole contents of the volume, with the exception of 

 the abstracts of Royal Institution lectures, have already appeared in 

 the pages of the Philosophical Magazine, any detailed comment upon 

 it would be out of place here, and we therefore content ourselves 

 with having thus announced its publication. 



