128 Dr Marshall Ward, The action of Light on Bacteria. [Nov, 27, 

 which we have already obtained, whilst (15) leads to 



2 r^ 2 r*'^ 



F=- sinh6'e-'-«'"h^(^6' + - cos 6' cos (r cos 6') (^6'... (17). 

 TTJo vrjo 



The last result might be immediately obtained from (14) by 



differentiation. 



(3) On Isotropic Elastic Solids of neai'ly Spherical Form. 

 Part I. Equilibrium. By C. Chree, M.A. [Published in the 

 Transactions. ^^ 



November 27, 1898. 

 Prof. T. M^K. Hughes, President, in the Chair. 



Dr F. H. H. Guillemard, Mr R Assheton and Mr J. W. 

 Capstick were elected Fellows of the Society. 



The following Communications were made to the Society: 



(1) The action of Light on Bacteria. By Dr H. Marshall 

 Ward. 



By throwing the spectrum on various bacteria suspended in 

 films of agar, it is possible to obtain photographic records of 

 the action of the various rays ; because, after incubation, those 

 spores or bacilli &c. which are killed by certain rays remain 

 invisible, whereas the colonies which are formed by the ger- 

 mination of those still left capable of development render the 

 agar opaque. The experiments show that those germs which 

 are struck by the infra-red, red, orange and 3^ellow develop as 

 rapidly as those not exposed to light at all. The action begins 

 as we leave the green, and rises to a maximum in the blue- 

 violet and violet, falling off as we pass into the ultra-violet. 



For the solar spectrvmi a heliostat and glass lenses and prism 

 were used ; for the electric spectrum a quartz train, and quartz 

 covering to the film. Even a thin plate of clear glass blocks out 

 much of the effective region of the spectrum, and especially ultra- 

 violet rays. 



The author records his thanks to Prof O. Lodge, F.R.S., for 

 kindly exposing the plates to the electric spectrum for him, with 

 most successful results. 



The author also found that the water of the Thames, examined 

 in August and in October respectively, shows the following in- 

 teresting results. 



1. The number of bacteria per c.c. was distinctly smaller 

 in the bright August weather than in the duller days of October, 

 and differences were observable in the aspect of the colonies on 

 plate-cultures. 



2. Suspecting that this was concerned with light action, 

 experiments showed that insolation not only kills off large 

 numbers of the bacteria in the water, but in some cases shows 



