ADDRESS. xlv 



Nautical Almaliae fof 1855' has been published this year. It is the first 

 American Nautical Almanac, and is considered to reflect great credit on the 

 astronomers of that country. It is under the superintendence of Lieut. C. 

 H. Davis, assisted in the physical department by Professor Peirce. 



No one has contributed more to the progress of Terrestrial Magnetism 

 during the last few years than my distinguisiied predecessor in this Chair. 

 Formerly we owed theories on this subject much more to the boldness of 

 ignorance than to the just confidence of knowledge ; but from the commence- 

 meut of the systematic observations which Colonel Sabine has been so active 

 in promoting, this vague and useless theorising ceased, to be succeeded, pro- 

 bably ere long, by the sound speculative researches of those who may be 

 capable of grappling with the real diflSculties of the subject, when the true 

 laws of the phaenomena shall have been determined. Those laws are coming 

 forth with beautiful precision from the reductions which Colonel Sabine is 

 now making of the numerous observations made at the different magnetic 

 stations. In his Address of last year, he stated to us that the secular change 

 of the magnetic forces was confirmed by these recent observations, and also 

 that periodical variations depending on the solar day, and on the time of the 

 year, had been distinctly made out, indicating the sun as the cause of these 

 variations. During the present year, the results of the reduction of the ob- 

 servations made at Toronto have brought out, with equal perspicuity, a va- 

 riation in the direction of the magnetic needle going through all its changes 

 exactly in each lunar day. These results with reference to the sun prove, as 

 Colonel Sabine has remarked, the immediate and direct exercise of a magnetic 

 influence emanating from that luminary ; and the additional results now 

 obtained establish the same conclusion with regard to the influence of the 

 moon. It would seem, therefore, that some of the curious phaenomena of 

 magnetism which have hitherto been regarded as strictly terrestrial, are really 

 due to solar and lunar, as much as to terrestrial magnetism. It is beautiful 

 to trace with such precision these delicate influences of bodies so distant, 

 producing phaenomena scarcely less striking either to the imagination or to 

 the philosophic mind, than more obvious phaenomena which originate in the 

 great luminary of our system. 



New views which have recently sprung up respecting the nature of heat 

 have been mentioned, though not in detail, by my two immediate predecessors 

 in the chair of the Association. They are highly interesting theoretically, 

 and important in their practical application, inasmuch as they modify in a 

 considerable degree the theory of the steam-engine, the air-engine, or any 

 other in which the motive power is derived immediately from heat; and it is 

 correct theory alone which can point out to the practical engineer the degree 

 of perfection at which he may aim in the construction of such machines, and 

 which can enable him to compare accurately their merits when the best con- 

 struction is arrived at. 



A theory which proposes to explain the thermal agency by which motive 

 power is produced, and to determine the numerical relations between the quan- 

 tity of heat and the quantity of mechanical effect produced by it, may be termed 

 & Dynamical theory of heat. Carnot was the first to give to such a theory a 

 mathematical form. His theory rested on two propositions which were re- 

 garded as axiomatic. The first embodied the abstract conception of a per- 

 fect thermo-dynamic engine, and has been equally adopted by the advocates 

 of the new theory of heat. Again, suppose a given quantity of heat to enter 

 a body by any process, and thereby to change its temperature and general 

 physical state ; and then, by a second process, suppose the bodv to be re- 



