2 9 o SCIENCE PROGRESS 



formula connecting vapour pressure and temperature, viz. 

 log p = A + Ba l + Cfi (where A, B, C, a, are constants), 

 one obtains an equation for the latent heat which fits the 

 facts very well for all the non-associated liquids which have 

 been examined. But if a similar process is applied to a slightly 

 modified van der Waals' formula (the modification being con- 

 sistent with the notion of a molecule expanding uniformly 

 with rise of temperature, a notion recently put forward in 

 other quarters), then the facts for non-associated liquids are 

 equally well summarised. Neither formula, however, seems 

 to agree with the facts concerning associated liquids. The 

 same number of the Phil. Mag. contains a paper by Dr. A. 

 Ferguson explaining a new empirical formula connecting the 

 boiling-points and the molecular weights of the normal paraffins 

 with considerable accuracy over a wide range, and also, for the 

 same series, empirical formulae showing the relation between 

 critical temperature and chemical constitution. 



When fusion of a pure metal takes place, there is, as is 

 well known, a sudden decrease in its electrical conductivity in 

 most cases. According to the well-known generalisation of 

 the Wiedemann-Franz law, there ought to be a corresponding 

 change in the value of the thermal conductivity. The June 

 number of Proc. Phys. Soc. London contains an investigation 

 by Prof. Porter and F. Simeon of this point. For mercury 

 and sodium they find that the change in the thermal con- 

 ductivity on fusion is of the same order as that of the electrical. 



Sound. — In the same journal there is a paper by Prof. 

 Morton and Miss Darragh on the origin of Combination Tones, 

 and a discussion of the theories bearing on it, one propounded 

 by Koenig and extended by Voigt, the other proposed by 

 Helmholtz and generalised by Everett. 



The magazines referred to above also contain descriptions 

 of apparatus for various purposes. A Duplex Harmonograph 

 for compounding four harmonic motions is described in the 

 April Phil. Mag. An instrument to measure air velocities, by 

 measuring the resistance of a hot wire lying in the air-current 

 (the Kelvin Double-Bridge being employed) also appears in 

 the same number. In the April Proc. Roy. Soc. Prof. Callendar, 

 W. A. Bone, and H.J. Yates show how the bolometer may be 

 adapted to the measurement of the efficiencies of radiating 

 surfaces such as gas-fires, electric radiators, incandescent 



