Researches on Heat. 267 



for the more numerous are the objects to which the attention 

 must be directed, the more likely is the chance of error arising 

 and increasing- from the intricacy of combination. In short, the 

 principles here set forth, if unacknowledged in the usual direc- 

 tions, must nevertheless be latent in any mode of approximating 

 to the true answer of this great problem in navigation ; it only 

 then remains to be desired, that the most compendious way of 

 so far solving it as is possible, may be adopted. 



In what was said, the meridian of the place was supposed to 

 have been already determined by one of the commonly practised 

 methods: as, however, there are times when no other heavenly 

 bodies but the stars are visible, it may not be deemed inapplicable, 

 to show how that spangled canopy alone affords sufficient clue for 

 finding the mid-heaven arch above any diameter of the compass. 



The subjoined rules depend upon the zenith point being cor- 

 rectly distinguished ; which is always the postulate of marine 

 observations. 



1st. It being known that two (or more) stars have the same 

 longitude, i. e. lie south and north of one another, when they are 

 in a line with the zenith the meridian coincides therewith ; and 

 when they are not in a hne with the zenith, yet a line drawn 

 through the zenith parallel to the line in which thev are is iden- 

 tical with the meridian. When sufficiently elevated and clear to 

 view, either pole and the zenith give the meridian line. 



2d. It being known that two (or more) stars have the same 

 latitude, i. e. lie west and east of one another, when they are 

 equally above the horizon, the line that joins them is to be equally 

 bisected by a perpendicular to the same, — the bisecting line is 

 in the plane of the true meridian. 



1819. W.W. 



XLIV. Researches on some important Points of the Theory of 

 Heat. By MM. Petit anc? Dulong*. 



Vy'ONViNCED that certain properties of matter would exhibit 

 themselves under simpler forms, and might be expressed by more 

 regular and less complex laws, could we but refer them to the ele- 

 ments on which thev immediately depend, we have endeavoured 

 to introduce into the study of some of the properties which ap- 

 pear more intimately connected with the individual action of the 

 material molecules, the most certain results of the atomic theory. 

 We are led to hope, from the success wc have already met with, 

 that the atomic theory will receive from our investigation a new 



• From Annulet de Chitnie ct Phys. tome x. 



degree 



