NATURAL PHILOSOPHY. 151 



years ; and these anticipations have been verified by the recent re- 

 searches of Le Terrier on the motions of the planet Mercury. Then, 

 from further considerations connected with the motion of comets, he 

 shows that this meteoric matter must be derived from spaces very 

 near to the "sun. He then proceeds to estimate how much the sun 

 cools annually, and concludes that it cannot be more than 1.4 Centi- 

 grade annually. He then shows, from facts derived from various 

 sources, chemical and astronomical, that the certain limits are entirely 

 inconsistent with some of Darwin's geological estimates of time. Under 

 the second head, the author shows that the statement which he first 

 made still holds, with undiminished force, that meteoric action is not 

 only proved to exist as a cause of solar heat, but it is the only one of 

 all conceivable causes which we know to exist from independent evi- 

 dence. The reasons for this are again given at length. And he con- 

 cludes it is, on the whole, most probable that the sun cannot have 

 illuminated the earth for 100,000,000 years, and certain that it has 

 not for 500,000,000 ; and as to the future, that the inhabitants of the 

 earth cannot continue to enjoy the light and heat necessary for their 

 existence for many million years longer, unless some sources now un- 

 known to us are prepared in the great storehouse of creation by Him 

 who orders all things rightly and well. 



NEW PYROMETER. 



Serious difficulties have hitherto presented themselves in the con- 

 struction of a really exact pyrometer. M. Noble, an engineer at 

 St. Petersburg, has long been engaged in the study of the heat 

 developed by furnaces of various kinds. As the result of his experi- 

 ments, he has recently brought out a very simple apparatus, most 

 easy of application and exact in its indications. This apparatus con- 

 sists essentially of a cylindrical vessel or chamber composed of plati- 

 num or other refractory substance, capable of withstanding a consid- 

 erable degree of heat. This chamber is connected by a tube with a 

 pressure-indicator or manometer. Bourden's is found to answer well. 

 The vessel is placed in the furnace, and the tube is passed through a 

 luted opening in the side thereof, and is connected at its outer end 

 with the manometer. By using a very sensitive Bourden's manome- 

 ter, and by adding thereto an apparatus for showing the number of 

 revolutions of the needle or indicator, the increasing temperature for 

 each degree will be readily arrived at, allowance being made, of 

 course, for the atmospheric pressure on the apparatus itself. 



THE PHENOMENON OF REGELATION. 



In the year 1850, Prof. Faraday directed the attention of scientists 

 to the remarkable fact that two pieces of moist ice, when placed in 

 contact, will unite, even when the surrounding temperature is above 

 Cent. To the phenomenon in question the term " regelation " has 

 been applied by Tyndall, who has made the fact above mentioned the 

 basis of a theory of the plasticity of ice, in accounting for the descent 

 of glaciers. Several theories have been advanced to explain the facts 

 of regelation. Faraday explained it by assuming that a particle of 



