8io 



NA TURE 



[December 16, 1922 



In the second place, the co-ordinate axes are 

 supposed to be normal to one another. How is this 

 normality to be denned? It is to be remembered 

 ■ i , mality in Space-Time theory is a wider 



conception than normality in ordinary geometry ; 

 since in the former we have lines which are " sel] 

 normal" (or what I have called "optical lines"), 

 111 addition to other rather curious features. 



1 n the third place, the co-ordinate axes are supposed 

 (if I may so express it), to be capable of graduation in 

 equal parts. How is this graduation to be theoretic- 

 ally arrived at, and how are we to compare lengths, 

 say along the axis of x, with lengths in some other 

 direction ? 



It thus appears that we are reasoning in a circle 

 if we attempt to give an analytical definition of 

 Space-Time geodesies on such a basis. 



The employment of generalised co-ordinates does 

 not free us from difficulties, for, if it gets us out 

 of one difficulty, it brings in another in its place. 



Thus, for example, if the " graduations " were 

 made according to arbitrary scales, the expression 

 for the length of a Space-Time interval would contain 

 functions the form of which would depend upon the 

 arbitrary character of the scales employed. 1 



Again, if measurement of intervals be regarded 

 as a fundamental conception, what is one to make of a 

 case where 



(#j - .v 2 ) 2 + (y x - v 2 ) 2 + (*i - z 2 y- - (<! - t 2 y =0, 



in which (x lM y lt z v /,) and (v.,, y.,, z 2 , t 2 ) are the co- 

 ordinates of two Space-Time points ? 



It must not be supposed that in raising these 

 objections to the ordinary methods of treating this 

 subject I am concerned only with destructive 

 criticism. 



My own answers to these difficulties are to be 

 found in my published work. 



In conclusion, I must thank Mr. Rogers for his 

 very interesting letter published in Nature of 

 November 25 ; which, however, does not call for any 

 special reply. 



Alfred A. Robb. 



Cambridge, November 27. 



A New Type of Electrical Condenser. 



Sixer, an electrical condenser is a device for storing 

 elei tin ity, it follows that a secondary battery is a 

 condenser — obviously of very large capacity as 

 compared with the electrostatic type of condenser. 

 Arguing from this point of view it appeared to the 

 writer that, by a suitable arrangement of pasted lead 

 grids immersed in dilute sulphuric acid and connected 

 in circuit with an alternating current, it should be 

 possible to obtain the characteristic effect of an 

 electrical condenser, namely, a phase advance of the 

 current relatively to the terminal potential differen< e 



A large number of tests have borne out this con- 

 clusion and it may be of interest to readers of Nature to 

 show an oscillogram of the effect (Fig. 1 ) . The oscillo- 

 gram was taken during a test on a cell consisting of grids 



1 This is the same sorl of point 

 thermodynamical theory by using s 

 nstead of the thermodynamic scale. 



NO. 2772, VOL. I IO] 



pasted with red lead and immersed in dilute sulphuric 

 acid. The temperature of the electrolyte was about 

 86° C, the frequency of supply was 3-5 cycles per 

 second, the current density about 0-75 amperes per 

 square inch of grid and the r.m.s. value of the terminal 

 pressure was a little more than 2 volts. There was 

 practically no gassing of the cell during the test. 



If the fundamental of the potential wave is deter- 

 mined it will be seen that there is a large angle of 

 phase advance of the current on the pressure. There 

 is <tne other interesting point noticeable in the oscillo- 

 gram, namely, the potential difference of the grids 

 remains relatively very small during a large portion of 

 the current wave. When the current wave has passed 

 its maximum value the pressure quickly rises to a 

 maximum and then falls to zero at about the same 

 moment as the current reaches its zero value. The 

 process is then repeated during the next half of the 

 current wave. T. F. Wall. 



Edgar Allen Research Laboratory, 



The University, Sheffield, November 25. 



[An engineering contributor to whom we have 

 shown Dr. Walls' interesting letter writes : " It 

 has been well known to electricians for the last 

 thirty years that an electrolyte with metal plates 

 in it will act as a condenser. These devices are 

 called electrolytic condensers and are used in every- 

 day work. They generally consist of aluminium 

 plates immersed in an electrolyte, but iron plates in 

 a solution of soda are sometimes used. They are 

 useful for getting currents which lead in phase the 

 supply voltage. Dr. Gunther Schulze carried out 

 an extensive series of tests on electrolytic condensers 

 at the Reichsanstalt in 1909. See Elektrotechnik 

 und Maschinenbau, ' Kondensatoren Grober Kapa- 

 zitat ' (vol. xxvii. p. 247, 1909)." — Editor, Nature.] 



Sex of Irish Yew Trees. 



After extensive inquiry up and down the country, 

 I have so far failed to come across any example of 

 the Irish Yew bearing male flowers. All the trees 

 examined in private gardens and in cemeteries and 

 churchyards have been of the berry-bearing or female 

 sex. 



I have now a number of young plants raised from 

 the berries of the Irish Yew (Taxus fastigiata) 

 fertilised by pollen from the English variety {Taxus 

 baccata). These show a graded series from the 

 spreading English type to the erect Irish form. 



Growth is so slow, however, that it will be some 

 years before it will be possible to ascertain the sex 

 of these plants ; meanwhile, 1 should be glad to know 

 through the readers of Nature any case of a male 

 Irish Yew. 



If, as is believed, the Irish Yew trees now growing 

 in England have all been propagated by cuttings from 

 the mutational Irish form, which first appeared in 

 Co. Fermanagh, Ireland, more than a hundred years 

 ago, this would explain the fact that they are all of the 

 female sex. On the other hand, it is desirable to 

 ascertain whether any linkage originally existed 

 between erect habit of growth and female-ness in the 

 mutational Irish variety. 



Further, if any male example of the Irish Yew can 

 be discovered it would be desirable to test the effect 

 of fertilising the female Irish Yew by Irish pollen. 



C. J. Bond. 



Fernshaw, Springfield Road, Leicester, 

 November 28. 



