628 REPORT— 1895. 



taneously escaping out of the other, the quantity of air escaping may be repre- 

 sented in the simplest case by such a formula as 



Q = C(l-sin27rm)f) {l-sm2Trnt) 

 = C [1 - sin 2n- vit - sin Stt nt + |^ {cos Srr (m — 7i)t — cos 2rr (m + n) t\ ], 



thus giving rise to the first difference and summation tones. 



A somewhat similar theory has since been elaborated by Terquem. (' Annales 

 d'Ecole Normale,' 1870, p. 356). 



At present it must be considered to be open to qiiestion whether the objective 

 combination tones given by the siren are due to finite displacement or to inter- 

 mittence, or to both causes combined. 



2. A Discussion ' on a New Practical Heat Standard.' Introduced by a Paper 

 by E. H. Griffiths, F.R.S. 



3. On the Thermal Conductivities of Mixtures of Liquids. 

 By Charles H. Lees, D.Sc. 



The author has carried out a number of determinations of the thermal conduc- 

 tivities of mixtures of liquids by a method analogous to that of Christiansen, but 

 with the heat supplied electrically and the temperature measured by means of 

 thermo-j unctions. For the mixtures of water, glycerine and alcohols experimented 

 on, the conductivities are found to be less than the values calculated from the 

 amounts and thermal conductivities of the constituents, and the author believes 

 that this will be found to be a general law. A possible explanation may be found 

 in the inability of one of the molecules of a mixture to take up and transmit the 

 particular kind of vibration executed by the other. 



For solutions of salts and gases in water the author finds conductivities less 

 than that of water, in agreement with the results obtained by Jager. 



4. A Method of Comparing the Heats of Evaforation of Different Liquids 

 at their JJoilinr/ Points. By Professor W. Ramsay, Ph.D., F.R.S., 

 University College, London, and Miss Dorothy Marshall, B.Sc, 

 University College, London. 



This method consists in making the liquid boil by passing an electric current 

 through a wire immersed in it. 



The liquid is put into a glass bulb enclosed in an outer jacket filled with 

 Tapour of the same liquid. An open tube is attached to the top of the bulb, so 

 "that there is free communication between the interior and the vapour jacket, and 

 •no loss of material. Inside the bulb is a spiral of fine platinum wire, attached to 

 •stout platinum terminals which are sealed into the glass. These terminals rest in 

 mercury cups, by means of which connection is made. The temperature of the 

 liquid in the bulb is raised to the boiling-point by the vapour jacket ; thus when a 

 current is sent through the wire the whole of the heat developed is spent in 

 converting a portion of the liquid into vapour. 



If two such bulbs containing difierent liquids are connected in series, the ratio 

 of their losses of weight is the inverse ratio of the heats of evaporation of the 

 liquids. 



A correction must be made for the inequality in resistance of the spirals. 

 The ratio of the differences of potential between the ends of each spiral while the 

 current is passing is determined in each experiment by PoggendorfT's method. 



