624 SCIENCE PROGRESS 



indicated. It might have been thought that it would have 

 been better to base the investigation upon observations of 

 Neptune ; this was not done because less than half of its orbit 

 has been described since it was first observed, whereas there 

 are observations of Uranus dating back to 1690, when it was 

 observed by Flamsteed (who, of course, was ignorant of its 

 identity). Consequently the orbit of Uranus is better known. 

 The mass of the planet is indicated as seven or eight times 

 that of the Earth's mass, and its stellar magnitude as about 

 twelve or thirteen. The next step lies with observation, and 

 the planet — if it exists — may be found either visually by its 

 visible disc, or photographically by its trail relative to the stars. 



PHYSICS. By J. Rice, M.A., Lecturer in Physics, University of Liverpool. 



In the Proc. Roy. Soc, December 191 5, Prof. Duffield gives a 

 description of experiments carried out by himself and some 

 pupils on the consumption of carbon in the electric arc. One 

 extremely interesting and very simple conclusion is arrived 

 at, viz. that when the arc length is extremely small, the loss 

 from the cathode of one carbon atom is accompanied by the 

 transfer between the poles of a quantity of electricity equiva- 

 lent to four electronic charges. For long arcs there is a further 

 loss of carbon due to combustion or evaporation. The loss 

 per coulomb for a given current density in the carbons increases 

 with increasing arc length until a nearly constant value is 

 reached at about 8 mm. This maximum value is to be 

 expected, as a limit is reached when increasing the length of 

 the arc does not augment the amount of air which by gaining 

 access to the hot poles causes oxidation. 



As is well known the anode loss is greater than the cathode 

 loss, a fact accounting for the existence of the crater ; the 

 ratio of the two losses varies for the same length of arc with 

 the current strength ; for long arcs Prof. Duffield finds the 

 ratio rises from 1*36 to 1*64 when the current varies from 2 

 amperes to 8 amperes. In long arcs the loss of material per 

 coulomb decreases with increasing current. This result is 

 opposite to what might have been expected, since so much 

 more heat is generated by the larger currents ; but it should 

 be observed that it is the loss of carbon per coulomb of 

 electricity which is in question ; with small currents the 



