166 Prof. Duffield and Mr. Littlewood on Correction of a 



Taking the structure of crystalline bismuth as similar tc~ 

 that of crystalline antimony^ Ave find from the above the 

 spacings of one of the sets of planes. 



The distances are in Angstrom units. 



(100) (110). (Ill) (110) (111) 



3-25 2-35 3-92 2*25 3-69 



The relative positions of the two sets of planes have not 

 been accurately fixed as the spectra were faint. The spectra 

 from the (111) face showed somewhat the same order of 

 intensities as those from the corresponding face of the 

 antimony crystal. It is hoped by more accurate observa- 

 tions of the ratios of these intensities to fix the spacings. 



Summary. 



Experiments confirm the conclusions of James and Tun- 

 stall that the unit rhomb contains 8 atoms, that the length 

 of the edge of the unit rhomb is 6'20 A. U., and that the 

 structure consists of two interpenetrating face-centred 

 lattices. 



The spacings of the planes, which differ somewhat from 

 those given by James and Tunstall, are given in fig. 1. 



The shortest distance between the centres of two atoms is 

 2-92 A. U. 



The unit rhomb of crystalline bismuth contains 8 atoms. 



The length of the edge of the rhomb is 6*52 A.U. 



The spacings of one of the face-centred lattices have been 

 calculated. 



XVI. The Correction of a Marine Barometer for Errors due 

 to Swinging. By Professor W. Gr. Duffield, D.Sc, and 

 T. H. Littlewood, M.A., Honorary Research Fellow in 

 Physics in University College, Reading* . 



(1) r I ^HE deviation of a barometer from the vertical 

 -«- position introduces an error which is likely 

 to be serious if the instrument is to be used for gravity 

 determinations, and which on occasion may be of signi- 

 ficance in meteorological work. For a steady deviation, a, 

 the height of the mercury in the stem will be measured 

 as Asec#, whence it is easily seen that for a deviation 

 of three degrees from the vertical the estimated pressure 



* Communicated by the Authors. 



