RECENT ADVANCES IN SCIENCE 467 



heaping up of other particles in its neighbourhood, and that an 

 accelerated body induces an acceleration of the same direction 

 in other bodies. These early speculations of Mach follow as 

 direct conclusions from Einstein's theory. 



At the same section, Dr. P. E. Shaw gave an account of his 

 experiments, which appear to indicate a change in the gravita- 

 tion constant with the temperature of gravitating bodies. Dr. 

 Shaw has already published a statement of his work in the 

 Phil. Trans. A. 216 (19 16). The experimental work has been 

 of extreme delicacy and has, it would appear, been going on for 

 close on ten years, some earlier types of apparatus having proved 

 of no avail in the research and having to be abandoned. The 

 apparatus ultimately used was of the Cavendish torsion-balance 

 type in the form adopted by Boys in his researches on the value 

 of the gravitational constant. The suspended system was 

 enclosed in a vacuum vessel in which the pressure of the resi- 

 dual air was varied from about 1 micrometre of mercury for 

 some experiments to as high as 1 5 millimetres for others. The 

 large masses of lead whose gravitating effect on the suspended 

 system was being observed had their temperatures altered by 

 electric heating between limits 15 C. and 250 C, the suspended 

 system being maintained at ordinary laboratory temperatures. 

 The utmost precautions were taken to guard against spurious 

 effects due to electrostatic or magnetic action, or to convection 

 in the residual air or its radiometric pressure, or even to the 

 radiation pressure of the lamp used to illuminate the mirror on 

 the suspended system. In the first instance it would appear 

 desirable to test if the gravitation constant varied according to 

 some expression linear in the mean temperature of the attracting 

 masses (each temperature being " weighted " by the corre- 

 sponding mass in obtaining this mean). On account of the large 

 mass of the lead spheres or cylinders in comparison with that 

 of the suspended system, this mean temperature would be 

 practically that of the lead bodies. Dr. Shaw is unable to 

 assert from his experiments that such a linear relation does 

 hold, but he states that he has been able " {a) to obtain con- 

 sistent cyclic readings in a gravitational experiment of the 

 Cavendish type, even though the large masses are maintained 

 for hours above 200 C, while small masses remain at ordinary 

 temperature ; (b) to carry on this investigation in the centre of 

 a city at any time by day or night, in spite of the attendant 



