168 AXXl'AL OF SCIEXTIFIC DISCOVERY. 



various degrees of heat, which mixed with each other and attained a certain 

 decree of temperature in the same manner as substances subject to all the 

 physical inlluences of the earth's exterior. 



Prof. Hennessy remarked that the views of Dr. Siljcstrom seemed to state 

 in other words the well-known fact, that a mass of fluid po-sessiiiL: different 

 temperatures in different parts of its interior must be subjected to a process 

 of convection. The result is usually a chanirc of volume in the entire ma-> 

 of circulating fluid. This change is capable of being observed in ordinary 

 experiments, and may also atfect the volume of the fluid matter in the inte- 

 rior of the earth, provided the changes of temperature of the fluid arc suffi- 

 ciently great. But it is clearly proved that the refrigeration of the earth is 

 now so extremely slow, that it is not likely that any considerable changes of 

 volumes arising from this cause could have arisen within recent period*. If 

 such changes have arisen, they must have occurred during remote geological 

 epochs. 



EXPERIMENT SHOWING THE CONTRACTION OF WATER THROUGH 



TEMPERATURE 



At a recent meeting of the Edinburgh Philosophical Society, an experi- 

 ment showing the contraction of water above the freezing point, was ex- 

 hibited. The water operated on was contained in a glass jar, about 4 inches 

 in diameter and IS inches high; and the changes in its density were shown 

 by the accent and descent of colored glass balls, about an inch in diameter. 

 Wlien the Avater was ice-cold the balls were all at the bottom; but gradually, 

 as the warmth of the room was communicated to the water, its contraction 

 and consequent increase of density caused the balls to rise. As the water 

 approached the state of greatest density, the heavier balls were seen to move 

 irregularly about, in consequence of the current caused by the changes of 

 temperature. In the course of an hour, the point of maximum density hav- 

 ing been passed, the balls began to descend in reverse order, and at last all 

 again reached the bottom. 



ON SOME PHYSICAL PROPERTIES OF ICE. 



In a recent lecture by Professor Tyndall before the Royal Institution on 

 the above subject, the author, after referring to the force by which crystalline 

 architecture is accomplished, exhibited some phenomena of crystallization by- 

 means of the photo-electric microscope. The manner in which the molecu- 

 lar aggregation was affected when a beam of radiant heat was sent into the 

 interior of a mass of ice, was examined. The track of such a beam pre- 

 sented a beautiful appearance flattened spheroids were observed, which at 

 certain incidences of the light shone with more than metallic brilliancy, and 

 around each a liquid flower, consisting invariably of six petals, was formed. 

 The spot at the centre of each flower was proved to be a vacuum, and the 

 formation of the flowers in a piece of ice through which a beam of electric 

 light was transmitted was rendered visible to the audience. The air and 

 water cavities, which, in the case of glacier ice, have caused so much dis- 

 cussion, were next examined. It was proved that the water Avas due to the 

 melting of the ice round the air cavities. The hypothesis pronounced by M. 

 Agassiz and the Messrs. Schlagintweit to account for this water, and which 

 lri< hitherto been universally accepted, is, that the ice permits the radiant 

 heat to pass, the heat warms the air, and it in its turn melts the it-e. It was 



