235 



spondence in the serrated form of the edges of the teeth, in the ridges 

 on their vertical surfaces, and particularly in the manner in which 

 the new teeth are formed in lateral cavities at the base of the fangs 

 of the old ones. 



From the nature of the fossils with which these teeth are asso- 

 ciated, the author concludes the Iguanodon to have been, if amphi- 

 bious yet not marine, but an inhabitant of rivers and fresh-water 

 lakes. Judging from the proportions of the recent iguana, he con- 

 cludes that some of the fossil teeth figured in his paper must have 

 belonged to an individual upwards of 60 feet long. 



The author then considers the vertebrae, which differ materially 

 from those of the recent iguana, crocodile, &c., and resemble rather 

 those of the fossil crocodiles of Havre and Honfleur, being depressed 

 at both extremities ; but, as among recent lacertae there are exam- 

 ples of the same structure in a higher degree, and the fossils in ques- 

 tion are clearly of the saurian type, he does not regard the discre- 

 pancy as sufficiently important to invalidate the conclusions attempted 

 to be established in this paper. 



An experimental enquiry into the Nature of the radiant heating effects 

 from terrestrial sources. By Baden Powell, M.A. F.R.S. of Oriel 

 College, Oxford. Read February 17, 1825. [Phil. Trans. 1825, 

 p. 187.] 



In this paper the author first states the opinion of various prece- 

 ding experimenters on the subject of the heat evolved from non-lumi- 

 nous sources, and from bodies in various degrees of luminosity, and 

 observes that all the facts may be accounted for, by supposing two 

 distinct heating influences, one associated in some very close way with 

 the rays of light, and carried as it were by them through a glass 

 screen without heating it, the other being merely simple radiant 

 heat affected by the screen, exactly as the radiant heat from a non- 

 luminous body. 



In order to examine the truth of this explanation, he observes fur- 

 ther, that it is not sufficient to observe the effects produced by the 

 intervention of the screen alone, we must combine this with an in- 

 quiry into the relations to surfaces of the portions of the heat stopped 

 and transmitted ; that is to say, we must endeavour to discover whe- 

 ther the portions differ in any other respect than merely in trans- 

 missibility. 



To this end the author institutes a set of experiments, whose ge- 

 neral principle he states to be, " taking different luminous hot bodies, 

 to expose to their influence two thermometers presenting, one a 

 smooth black surface, the other an absorptive white one : thus ob- 

 taining the ratio of their total direct effects on the two, we may com- 

 pare it with the ratio similarly observed, when a transparent screen is 

 interposed." 



After noticing some causes of fallacy necessary to be guarded 



