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Considering this curious structure of the nose in an animal which 

 lives in water, it is natural to conclude that nature has fitted it for 

 discovering its prey in that element, by means of the sense of smell ; 

 and that for this purpose it is enabled to introduce this prominence into 

 the small recesses in which its natural food is probably concealed. 



Experiments on the solar, and on the terrestrial Rays that occasion 

 Heat ; with a comparative View of the Laws to which Light and 

 Heat, or rather the Rays which occasion them, are subject, in order 

 to determine whether they are the same, or different. By William 

 Hersche\,LL.D.F.R.S. Part II. Read November 6, 1800. [Phil. 

 Trans. 1800, p. 437.] 



In the first part of this paper * the Doctor had proposed the seven 

 following points which he meant to elucidate in this inquiry. 1 . That 

 heat, both solar and terrestrial, is a sensation occasioned by rays 

 emanating from candent substances. 2. That these rays are subject 

 to the laws of reflection. 3. That they are refrangible. 4. That 

 they are of different refrangibility. 5. That they are liable to be 

 detained in their passages through other bodies. 6. That they are 

 also liable to be scattered on rough surfaces. And lastly, he pro- 

 posed to ascertain whether in a certain degree of energy these rays 

 may not have or acquire a power of illuminating objects. The three 

 former points have been considered in the first, and the four last are 

 the subjects of the present part of the paper. 



Concerning the different refrangibility of the rays of heat, being 

 the subject of the fourth article, we find that in refracting the rays 

 of the sun by a prism, two distinct spectra may be said to be pro- 

 duced, the one of light, and the other of heat, the latter being di- 

 stinctly observable by means of thermometers. These two spectra 

 the Doctor has found means to represent by a figure, in which the 

 length of the luminous or coloured spectrum, being represented by a 

 line on which are raised ordinates proportionate to the quantity of 

 illumination of each coloured ray, the curve joining these ordinates, 

 together with this base line, inclose an area which may be said to 

 represent the extent and intensity of the coloured rays. Adopting 

 now another base line of the length of the range of the refracted rays 

 of heat, one extremity of which is found to coincide with the termi- 

 nation of the coloured spectrum at the outward edge of the violet 

 ray, and the other to project beyond the opposite termination at the 

 red ray, which makes this line longer than the other, in the pro- 

 portion of nearly 5| to 3. Ordinates are here in like manner applied 

 according to the different degrees of intensity of heat indicated by 

 accurate thermometers, and thus another area is produced, which 

 represents the spectrum of heat both as to extent and intensity. On 

 inspecting these figures, parts of which coincide, but other parts 

 considerably deviate from each other, we find that the coloured and 

 the heating rays differ widely, both in their mean refrangibility and 

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