220 Intelligence and Miscellaneous Articles. 



and interesting matters. The book is accompanied by a fair index 

 and a very necessary glossary of terms and symbols ; for our 

 author has a fad, and some of his work reminds us of the Appendix 

 to Dodgson's ' Euclid and his Modern Kivals,' in which those who 

 know, know that there are many things hard to be understood. 



XXXI. Intelligence and Miscellaneous Articles. 



ON LEIDENFEOST'S PHENOMENON. BY K. S. KEISTENSEN. 

 ^HE author proves that the heat conveyed from the heated dish to 

 -■- the drop is not sufficient to explain the Leidenfrost phenomenon, 

 but that the heat transmitted by conduction of the vapour must 

 also be taken into account. Taking the temperature of the dish 

 at 200°, that of the drop at 100°, aud assuming that each are per- 

 fectly black, and that the conductivity of aqueous vapour is equal 

 to that of air, the quantities of heat transferred by conduction 

 and radiation are equal, if the distance between the dish and the 

 drop is 0*135 centim. As the assumptions for the radiation are 

 too favourable, the quantity of heat transmitted by conduction cer- 

 tainly preponderates. — Tidsshrift for Physik og Chemie[2~] ix.'p. 161 ; 

 Beibldtter der PhysiJc, xiii. p. 155. 



DETEEMINATION OF THE CHANGE WHICH THE INTEKNAL FEICTION 

 OF AIE EXPEBIENCES AT DIFFEEENT TEMPEEATUEES AND 

 UNDEE VAEIOUS PEESSUEES- BY P. DE HEEN. 

 A brass tube 2 cm. wide and 85 cm. long, closed at both ends, 

 carefully polished on the inside, is placed in an oil-bath, and a 

 light brass cylinder 8*5 cm. in length is allowed to fall through. 

 The diameter of the cylinder is about 0*35 mm. smaller than the 

 clear width of the tube, so that the air on the fall of the cylinder 

 must pass through an annular capillary slit. To the cylinder is 

 attached an iron wire, so that it could be held up by an electro- 

 magnet ; it was allowed to fall, and the time measured which 

 elapsed before it struck against the bottom of the tube. Neglecting 

 any possible friction of the cylinder against the sides of the tube, we 



have rj =T. const., 



where r\ is the coefficient of internal friction of air. The temperature 

 was varied from 0° to 300°, the pressure of the air enclosed in the 

 brass tube varied from 1 to 2280 cm. of mercury. In agreement with 

 earlier observers with the exception of M. Hirn, the author finds 

 that at the pressure of the atmosphere the internal friction of the 

 air increases as the two thirds power of the absolute temperature. 

 The variation of friction with the temperature appeared to have 

 a maximum at 300 mm. pressure. The dependence of the internal 

 friction on the temperature between 10 and 78 mm. pressure, as 

 follows from the author's experiments, may be very well expressed 

 by the ratio required by Clausius' theory ; that is, proportional to 

 the root of the absolute temperature, which above 80 mm. pressure 

 is no longer the case. — Bull. Ace. Belg. [3] xvi. p. 195 ; Beibldtter der 

 PhysiJc, xiii. p. 124. 



