164 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



sound. If, for example, a plain wall were covered with 

 small projections, there would be a diffused echo due to the 

 projections, and an ordinary echo obeying the law of reflec- 

 tion. In the latter echo, the original will be faithfully re- 

 produced. In the diffused echo the higher elements, or the 

 waves of higher pitch, will preponderate, and according to 

 tlie relative strength of the diffused and the reo^ular echo 

 will be the impression made upon the ear of the hearer. 12 

 A, 1873, 300. 



IIINKICHS' THEORY OF MOLECULES. 



Hinrichs, of Iowa, has, in his "Molecular Mechanics," given 

 the physical properties of bodies as a function of the atomic 

 weight, and the moment of inertia of the molecules, and he 

 has recently sought to determine, experimentally and quan- 

 titatively, the existence of these physical properties. He 

 communicates his result to the Paris Academy of Sciences as 

 follows : According to his theory, the specific heat, the specific 

 volumes of the temperatures of boiling and fusing, are all def- 

 inite and simple functions of the moment of inertia of the 

 molecules ; and, by a process of computation which he de- 

 velops at length for the case of a certain class of hydrocar- 

 bons, he arrives at the conclusion that the maximum value 

 of the moment of inertia of a molecule of these bodies is 81.5 

 imits of an empirical scale adopted by him. 6 J^, 1873, 1592. 



THE DIALYSIS OP VEGETABLE CUTICLES. 



According to Barthelemy, the cuticle of a vegetable is a 

 natural colloidal film, through which carbonic acid gas is ab- 

 sorbed into the plant by a process similar to that first ob- 

 served by Graham, and called by him the phenomenon of 

 dialysis. The experiments of Professor Graham were made 

 upon thin solutions of various substances, almost exclusively 

 of vegetable origin, and also on easily soluble substances, to 

 which lie gave the name of crystalloid. Thus, for instance, 

 gruel or broth, containing a very little arsenic dissolved in 

 it and submitted to dialysis, gives up the whole of its arsenic 

 to the pure water on the opposite side of the dividing film 

 separating the gruel from the pure water. The film probably 

 acts upon different substances with diffei-ent degrees of in- 

 tensity, depending upon their relative chemical natures, and 



