( 793 ) 



Xous en comiaissons de iioinbreiix exemples '). If the stated plie- 

 noraena are connected with each other the conformity to the earliei' 

 process of development of the set of teeth of tlie Primates as I take 

 it, immediately strikes the eve; and one would be inclined to this 

 thesis; In the future set of teeth of man I\ -will no longer erupt, 

 7H3 will have become persistent and functionate as J/j, but by the 

 simultaneous reduction of J/, the number of molars will not have 

 become larger than three. 



So from this communication appears that the difterentiation of the 

 entire set of teeth of the Primates is from my standpoint more in- 

 tricate than was supposed till now, but it seems to me that my 

 principle of the terminal reduction can better be brought into accord- 

 ance with the function of the set of teeth, and is based on a 

 larger number of facts than the hypothesis of the excalation. 

 What from a general point of view, also seems to me to plead 

 for my opinion is the fact, that in the exposition given by me the 

 development of the set of teeth has taken place without a disconti- 

 nuitv in the toothrows at anv time. 



Physics. — "A simple geometrical deduction of tlie relations existing 

 between knoion and unknown quantities, mentioned in the 

 method of Voigt for determining tlie conductibility of heat 

 in crystals. By Dr. F. M. J.\eger. (Communicated by Prof. 

 P. Zeeman.) 



(Gommunicated in the meeting of March 31, 1906). 



It is commonly known that about ten years ago W. Voigt '^) 

 indicated a method, based on a recognized principle of Kirchhoff, 

 by which to determine the relative conductibility of heat in crystals 

 in the different directions. His mode of experimental examination 

 consists in the determination of the break which two isothermal lines 

 present at the boundary line of an artificial tw^in, the principal 

 directions of which form a given angle <f with that line, whilst the 

 conduction of heat takes place along the line of limit. The isothermal 

 lines are rendered visible to the eye by the tracings formed by the 

 fusion of a mixture of elaidic acid and wax with which the plane 

 of tlie crystal has previously been covered. 



1) E. Magitot. Traite des Anomalies du Système dentaire. Paris 1877. p. 221. 

 =) Voigt, Gottinger Nachrichten, 1896, Heft 3. 



