January 21, 19 15] 



NATURE 



561 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manusctipts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



Electrical Notation. 



The variety of notations for electrical quantities has 

 become a real difficulty in reading international litera- 

 ture. Up to the end of last centur>' the notation of 

 Maxwell was the standard in Great Britain, and such 

 extensions as became necessary* were grafted on it. 

 There is no sign of its dying out among the workers, 

 many of them of fundamental importance, who have 

 been accustomed to employ it— in pure science at any 

 rate. 



You direct attention (p. 541) to the conflicting 

 recommendations produced simultaneously by two 

 committees, each carrying authority. As the list 

 which you reproduce on p. 545 claims to have inter- 

 national force, it would be interesting to speculate 

 how many readers could guess what are the quantities 

 proposed to be denoted by the symbols ?j, /, G. e, X, 

 Z, S, *. A German equivalent for / is given as v, 

 which is usually synonymous with n further up in the 

 table ; so that / seems to be a duplicate. 



Cambridge, January 15. J. Larmor. 



The Influence of Icebergs on the Temperature of the 

 Sea. 



The part of the " Report on the work, carried out 

 by the s.s. Scotia, 1913," on the above subject, re- 

 ferred to in Nature of January 14, will, I fear, be a 

 great disappointment to many after the great 

 promise given by the new line of investigation dis- 

 covered by Prof. H. T. Barnes, of Montreal Uni- 

 versity. Prof. Barnes found, by means of a verj- 

 sensitive registering thermometer, that there was 

 always a rise in temperature of the sea on approach- 

 ing icebergs, and part of the Scotia's work was to 

 check this observation. The Scotia was fitted with 

 two sensitive registering thermometers, one to be 

 used for trawling near the surface ; the other was 

 placed in a box through which the condenser water 

 for the engine was pumped. Unfortunately, both 

 these instruments soon became defective owing to 

 sea water leaking into them. The one used for 

 surface temperatures was repaired on the voyage, 

 but the other does not seem to have been restored 

 to working condition. The result is that all the 

 temperatures taken with the recording instrument 

 are surface temperatures taken at a depth of 2 ft. 



The following is the conclusion come to by the 

 observers on the Scotia. " An inspection of the 

 records . . . leads to the conclusion that the tempera- 

 ture of the sea near its surface does not furnish a 

 certain method of detecting the presence of an ice- 

 berg in the regions over which the Scotia made her 

 voyages." Now Prof. Barnes's conclusion was not 

 arrived at from temperatures taken near the surface, 

 but at some depth. His records of the rising tempera- 

 ture on approaching icebergs were made with his 

 first ship, in which the thermometer was placed at a 

 depth of 5 ft., but better results were obtained by his 

 second ship, in which it was placed at a depth of 16 

 to 18 ft. 



In justification of their conclusion that their surface 

 temperatures ought to give results similar to the 

 deeper ones, the observers on the Scotia seem to have 

 accepted Prof. Barnes's explanation of the cause of 

 the rise in temperature near the berg. Prof. Barnes 



NO. 2360, VOL. 94] 



says all the water from the melting ice is carried 

 downwards, and that this downward current is 

 supplied by a surface current flowing towards the 

 berg, and that this surface current, in some way not 

 explained, retains all the solar radiation, which he 

 says usually penetrates deeper, but is, he says, pre- 

 vented by the water being in motion. If that ex- 

 planation be correct, then the Scotia's observers would 

 be quite right in supposing that the rising tempera- 

 ture would be more manifest at the surface than at 

 some depth. Though the Scotia's observers accepted 

 Prof. Barnes's explanation of the heating of the 

 water, they do not seem to be satisfied with it, as 

 they say : " This explanation is difficult and seems 

 complicated." 



Prof. Barnes's explanation is founded on the sup- 

 position that all the water of the melted ice is carried 

 downwards. Dr. Otto Pettersson, on the other hand, 

 says that only the water of the ice melted some 

 distance below the surface is carried downwards, while 

 that melted near the surface flows away from the berg 

 on the surface. In a previous letter (Nature, 

 Januar\' 9, 19 13) I showed by two methods of experi- 

 menting that all the water of the melted ice comes 

 to the surface. I think it is generally admitted that 

 the salinity of the sea is, as a rule, lower in the 

 vicinity of melting ice than at a distance from it. If 

 so, where does the fresh water come from if not from 

 the melted ice? Outside the rising current of diluted 

 sea-water next the ice there is a descending radiation- 

 cooled current of sea-water drawn from a distance 

 and flowing underneath the ice-cooled water on the 

 surface. This downward current is accepted by Prof. 

 Barnes and Dr. Pettersson, though Prof. Barnes 

 does not admit the existence of the cold-surface 

 current. Accepting the existence of these currents in 

 the water surrounding icebergs, the following explana- 

 tion was offered in Nature (Slarch 16, 1913) of the 

 rising temperature observed on approaching icebergs. 

 The surface water at a distance from a berg has a 

 higher temperature than the water immediately under- 

 neath it. That is, outside the influence of the berg 

 the temperature decreases with the depth, so that 

 when the surface water is submerged by the cold- 

 surface current, it is sunk to some depth beneath the 

 surface, the result of this being that a thermometer 

 sunk to a depth of, say, 16 ft. when at a distance from 

 the berg registers a lower temperature than if placed 

 in the surface water; but if the deeply submerged 

 thermometer be moved into the water near the berg, 

 it will now register a higher temperature than it did 

 at a distance from it, because it will now be in the 

 I submerged-surface water, the temperature of which 

 will probably have fallen to some extent in its passage 

 under the cold-surface water. The effect of the 

 movement of the ship towards the berg is virtually 

 the same as raising the thermometer towards the 

 surface when the ship is outside the influence of the 

 berg. In the letter referred to I suggested the use 

 of two thermometers, one near the surface, the other 

 at some depth, and registering together, when an 

 inversion of the temperature would indicate the 

 approach to ice, if the explanation be correct. If 

 this inversion of temperature really does exist, it 

 might be detected by the ordinary tilting thermo- 

 meters, one in the water near the surface, and others 

 at depths down to three or four fathoms, as the 

 difference that might be looked for from Prof. Barnes's 

 thermograms amounts at times to a degree or more 

 Centigrade, an amount easily detected by means of 

 thermometers of that kind. 



It is a great misfortune that the thermometer in 

 the condensation water of the Scotia could not be 

 repaired for the investigation. The depth at which 



