180 



SCIENCE 



[Vol. LV, No. 1416 



The commonwealth or the accused may take 

 such oral or written proof for or against the 

 accused as it may deem it the best to present 

 these facts. 



This act to be in full force and effect from and 

 after its passage and approval as provided by 

 law. 



Arthur M. Miller 

 XJniversitt op Kentucky, 

 Febrtjart 8, 1922 



RELATIVITY AND STAR DIAMETERS 



To THE Editor of Science : That Michelson's 

 wonderful measurements on star diameters 

 have a fundamental bearing on Einstein's 

 theory and are capable of affoi-dint? a more 

 decisive proof of it than even the eclipse ex- 

 periments does not seem to be yet appreciated. 

 In my former note of March 25th, 1921, I ex- 

 pressed the hope that some one more competent 

 than myself would discuss the subject; but 

 nothing has so far appeared but a short note 

 by Dr. Burns, and as he appears to be under 

 some misconception of the theory, I ■will, with 

 the Editor's permission, go into it a little more 

 in detail. 



Dr. Burns refers to an acceleration in the 

 direction of propagation. But this field has 

 nothing to do with the measurement of the 

 diameter. What we do, virtually, is to divide 

 the star disc F into halves by the diameter, 

 shown as a dotted line, and take the centers 

 of gravity of the two semi-circles as two sources. 

 Obviously a considerable amount of the light 

 will come from the edge, as at E, and all of 

 it, except that coming from the diametric line, 



will be pulled sideways towards 



the diameter. 



By Einstein's theory light 



from a source S to an observer 



will be curved in the manner 



0^\ shown, since all world lines are 

 F ) warped in the neighborhood of 

 J matter. Dr. Burns's statement 

 that there is no warping of the 

 \ light from the star disc means 



U that light originating from a 



prominence E on the star would 

 \ not be warped, while light trav- 



\ eling past it, originating from 



an outside source S would; which necessitates 

 an ether between P and ; which is contrary 

 to the theory of relativity. 



The really important point, which I had 

 hoped to bring out in the discussion, is that 

 a purely gravitational bending, shewn by the 

 dotted line C, is not a mere warping, but a 

 permanent change of path to a sort of hyper- 

 bola. If the light bending were a purely gravi- 

 tational effect, all stars should shew measure- 

 able diameters, if above certain dimensions. 

 But they do not appear to do so. As the only 

 two alternatives seem to be gravitational bend- 

 ing or Einstein's theoiy, this seems to be a 

 definite proof of the theory. 



But we need a quantitative discussion, at, as 

 I have said, the hands of men better qualified 

 than myself. Mere guess work is not enough. 

 It is true that the angular effect of the world 

 line warping changes with distance, being 

 twice the gravitational effect, but the 

 amount of warping by the sun is approxi- 

 mately 11/2 seconds, while the total angle sub- 

 tended by Betelgeuse is only 1|30 of this, and 

 Betelgeuse is somewhere around ten million 

 times the size of the sun. A quantitative cal- 

 culation is necessary, not only for Betelgeuse 

 but also for those stars which shew no meas- 

 urable disc, to explain the absence of a meas- 

 urable gravitational bending, if Einstein's 

 theory is not true. 



Reginald A. Pessenden 



PRELIMINARY NOTE ON THE ETIOLOGY 

 OF POTATO TIP-BURN 



During the past two years investigations 

 have been carried on at the Experiment Station 

 of Pennsylvania State College to determine the 

 etiology and specificity of the potato tip burn 

 caused by the feeding of the potato leaf hopper, 

 Empoasca mali Le B. 



These experiments were in the form of a 

 series of inoculations with aqueous and alco- 

 holic extracts of E. mali Le B, and other potato 

 feeding insects. The inoculated plants were 

 exposed to sunlight of varied intensity by the 

 use of glass and mesh cages to detennine the 

 role of sunlight in the development of the 

 disease. 



