6^8 



NATURE 



[February io, 1916 



forms part of the system of seven great perennial 

 canals distributing the flow of the Jhelum, Chenab, 

 Ravi, and Sutlej Rivers in an equable and scientific 

 manner over 17,000 square miles of country, other- 

 wise, and formerly, only suitable for the raising of 

 camels and beasts of pasture, but now adapted to agri- 

 cultural development. The irrigation area of the seven 

 canals already exceeds 4^ million acres, i\ millions 

 of which are devoted to wheat and | million to cotton. 

 When fully developed, the triple canal scheme will 

 add another if millions acres to the total. The neces- 

 sity for the perennial canal system arises from the 

 fact that in the Punjab there are two distinct agri- 

 cultural seasons and two annual crops, both essential 

 to the successful financial working of the land. Dur- 

 ing the first of the seasons, that is, in the six hot 

 months (April to September) the ground is plentifully 

 supplied with moisture from the melting snows of the 

 Himalayas, in conjunction with the ordinary rainfall. 

 In the second six months, the cold period, the rainfall 

 is at a minimum and the rivers carry but low supplies. 

 The conservation and uniform distribution of the water 

 is, accordingly, a matter of extreme importance. The 

 introduction of the canals has been attended by very 

 satisfactory results, and the complete realisation of the 

 project will, it is hoped, prove, from an economical 

 and administrative point of view, a success of consider- 

 able magnitude. 



"When the accelerations of three points of a rigid 

 body are given, the acceleration of any point is 

 known." This statement has been partly verified by 

 Burmeister and others. In the Bulletin of the 

 American Mathematical Society (vol. xxii., 3) Pfof. 

 Peter Field shows that the problem can be solved very 

 simply by using the expressions for the accelerations 

 which are ordinarily given in text-books on mechanics, 

 and by this method the kinematical meaning of the 

 solution is also evident. 



The attempts to obtain a hydrodynamical solution 

 of the problem of eddy formation in the wake of a 

 moving solid have hitherto met with only very partial 

 success. A solution was attempted by Von K^rm^n 

 for motion in two dimensions on the hypothesis that 

 a steady motion exists in which the vortices retain 

 the same arrangement relative to the body. In a 

 paper in the Proceedings of the Royal Society of 

 Edinburgh (vol. xxxv., i, No. g) Mr. H. Levy has now 

 shown that such a distribution can never be stable. 

 Unfortunately, the pressure equation, which the 

 autlwr describes as "a necessary condition in any 

 hydrodynamical problem," is incorrect except in cases 

 of steady motion, of which the present is not neces- 

 sarily one, and the results therefore appear to require 

 further confirmation. 



The problem of the personal equation is always 

 interesting, but somewhat elusive of direct estimation 

 in complfex operations. In the Psychological Review 

 (vol. xxiii.. No. i) J. H. Harris records the results ot 

 some experiments which he has conducted for some 

 time on subjects engaged in estimating moderately 

 large samples of bean seeds, either for germination 

 tests or for determining the mean weights for different 

 seeds. The advantage of the method lay in the fact 

 NO. 2415, VOL. 96] 



that the subject could compare his estimate with the 

 true value, and so attempt to profit by his experience. 

 As a result of many observations and careful computa- 

 tions, he finds that the personal equation is remarkably 

 little affected by experience, while, on the contrary, 

 steadiness of judgment is unmistakably influenced by 

 previous experience. 



Part i of vol. xii. of the Bulletin of the Bureau of 

 Standards contains an account of an examination of 

 twenty radiation pyrometers by Messrs. G. K. Burgess 

 and P. D. Foote, of the bureau. All the ordinary types 

 of instrument were tested, and from the results ob- 

 tained a number of general conclusions are drawn. In 

 general, radiation pyrometers behave not as perfectly 

 black, but as grey bodies, and the law connecting the 

 indication of the instrument with the temperature of 

 the source deviates from the fourth power by plus or 

 minus 05. The principal errors of the instruments 

 examined were due to faulty design and construction, 

 but dirty or oxidised mirrors may produce errors of the 

 order of 100° at 600° C. Smaller errors may arise 

 owing to stray reflections, convection currents, and 

 wrong focusing. The types of black-body furnaces in 

 use at the bureau are described, and some account 

 is given of the use of the pyrometers for the estimation 

 of the temperatures of non-black bodies. 



We have received a reprint of an interesting article 

 on telegraphic transmission, contributed by Major 

 W. A. J. O'Meara to the Royal Engineers' Journal. 

 He points out that during the past seventy years or 

 so, although great improvements have been made, the 

 source of energy almost universally employed for trans- 

 mitting the signalling wave impulses is at constant 

 potential so that square-topped waves are sent. The 

 sine wave, he is convinced, would be preferable. He 

 supports the views to this effect recently expressed by 

 Lieut.-Col. Squier in a paper before the Physical 

 Society. The sine wave is the only one which can 

 pass through the cable without changing its character- 

 istic form, and the harmonics required to build up the 

 impressed square-topped wave are absorbed in the 

 cable, and merely represent a surplus charge for each 

 signal, which must be got rid of before the succeeding 

 signal can be sent. Lieut.-Col. Squier's proposal Is 

 to utilise an uninterrupted alternating current of pure 

 sine wave form, and to alter the impedance of the 

 transmitting circuit at the zero point of the wave. 

 This will alter the amplitude, and by making each 

 semi-wave of either sign represent an elemental signal, 

 but giving the dot twice the amplitude of the space 

 semi-wave, and the dash twice the amplitude of the 

 dot, the Morse alphabet can be sent with the maximum 

 rapidity and efficiency. 



Referring last week (p. 633) to Messrs. Isenthal 

 and Co. 's new list of rheostats, we expressed the hope 

 that they would continue to manufacture the resist- 

 ances in England after the war. Messrs. Isenthal 

 believe that even if after. the war the present strong 

 feeling against German-made goods should somewhat 

 subside, a great many of their clients will always 

 prefer to buy the British-made article. Moreover, 

 having invested a not inconsiderable sum in the neces- 

 sary machinery, press tools, and jigs required for the 



