Intelligence and Miscellaneous Articles, 237 



account for this. Such changes, in fact, may have produced all the 

 mutations of climate which the researches of geologists reveal." 

 (Philosophical Magazine, Oct. 1861, p. 277.) 



In the American Journal of Science for November 1863 (p. 398), 

 I have in this connexion referred to a paper by the late Major E. B. 

 Hunt, United States Engineers, " On Terrestrial Thermotics," pub- 

 lished in the Proceedings of the American Association for the Ad- 

 vancement of Science for 1849. In this paper Major Hunt argues 

 that the temperature of the earth's surface increases with the weight 

 of the barometric column, and that, as the atmospheric mass must 

 have been greater in the earlier geological periods by the amount of 

 carbon and of carbonic acid since abstracted, the temperature of the 

 earth must then have been higher. To this mass Prof. Dana would 

 add the abundant moisture of the insular climate of former times. 

 The augmentation of barometric pressure dependent upon these addi- 

 tions to the atmosphere would, however, probably be very inadequate 

 to explain the considerable differences in climate of which geology 

 affords us evidence ; and it is only in the light of your recent disco- 

 veries that the chemical constitution of the early atmosphere of our 

 globe enables us to explain the warmth of ancient climates. 



The object which I have in writing this note is thus not only to 

 set forth Major Hunt's early attempts to solve the problem, but to 

 call public attention to the fact that what I conceive to be its true 

 solution was first suggested by yourself. 



I have the honour to be, my dear Dr. Tyndall, 



Very faithfully yours, 



T. Sterry Hunt. 



ON THE INTENSITY OF SOLAR RADIATION IN DIFFERENT 

 SEASONS. BY FATHER A. SECCHI. 



Several meteorologists have introduced the use of a blackened 

 thermometer exposed to the sun for obtaining data on solar radiation. 

 Having myself used this instrument, I am convinced that no certain 

 conclusions can be obtained with it, for the temperature depends on 

 several circumstances which it is impossible to measure specially. 

 It depends in fact, (1) on the direct solar radiation ; (2) on the radia- 

 tion of surrounding objects ; (3) on the radiation of the air; (4) on 

 the agitation of the atmosphere. Yet as this element is of great 

 importance, and it is desirable to simplify this class of observations 

 so as to make them commoner in different climates, I have endea- 

 voured to improve this instrument by introducing into its use prin- 

 ciples already employed by some other observers, and especially by 

 Mr. Waterston. 



My apparatus consists of a metallic reservoir formed of two con- 

 centric cylinders of different diameters, the annular space of which 

 is filled with water. The internal cylindrical space is empty, and 

 free and open at both ends to receive the solar rays. In the axis of 

 this cylinder, by means of a tube which traverses the annular space 



