CONTENTS 
Page 
Physics. — Note on X-Ray SmcHRA . By Duane and R. A. Patterson 85 
Physics. — A Nbw Method op Using X-Rays in GrI^^tal Anai^ysis 
By G. L. Clark and W. Duane 90 
Physics.— Acoustic Topography Varying with the Position of the Organ 
PiPB . . . . . . . . By C. Barus 96 
Physics. — On Steering an Automobii^e around a Corner . By A. G. Webster 100 
Statistics. — The Probable Error of the Vital Index of a Population . 
By J. R. Miner 106 
Petrology. — The Average Chemical Compos*tion of Igneous Rocks . 
By F. W. Clarke and H. S. Washington 108 
Astronomy. —Dark Nebulae . . - • By H. N. Russell 115 
