450 EEPOKT — 1881. 



given above may possibly need correction at some future date, but as no 

 radical change affecting the accuracy of the instrument has been made, it 

 is assumed the values here given are not far from the truth. 



Owing to the unsuitabiJity of the instrument for the registration of 

 phenomena of very brief duration it is not jiossible to give any values 

 for the tensions observed during periods, of great electrical disturbance, 

 such as thunder or hail storms ; it may, however, be remarked that on 

 such occasions the deflections of the needle far exceed the limits of regis- 

 tration of the electrograph, which are from about — 150 to + (JOO volts. 



Excursions of the dot of light through a considerably larger range 

 than the above may be watched taking place with every flash of lightning 

 during a storm, but the rate of movement across the paper is far too 

 rapid to permit of photographic registry. 



Magnetic disturbances and aurorte are not found to produce any- 

 marked changes in the indications of the instrument. 



On the Arrestathon of Infusorial Life by Solar Light. 

 By Professor John Tyndall, F.R.S. 



[A communication ordered by the General Committee to be printed in cxienso 



among the Reports.] 



Three years ago I bi'ought with me to the Alps a number of flasks 

 charged with animal and vegetable infusions. The flasks had been boiled 

 from three to five minutes in London, and hermetically sealed durmg 

 ebullition. 



Two years ago I had sent to me to Switzerland a batch of similar 

 flasks containing other infusions. On my arrival here this year, one 

 hundred and twenty of these flasks lay upon shelves in my little library. 

 Though eminently putrescible, the animal and vegetable juices had re- 

 mained as sweet and clear as when they were prepared in London. 



Still an expert, taking up one of the flasks containing an infusion of 

 beef or mutton, would infallibly pronounce it to be charged with organisms. 

 He would find it more or less turbid throughout, with massive flocculi 

 moving heavily in the liquid. Exposure of the flask for a minute or two 

 to lukewarm water would cause both turbidity and flocculi to disappear, 

 and render the infasion as clear as the purest distilled water. The 

 turbidity and flocculi are simply due to the coagulation of the liquid to a 

 jelly. This fact is some guarantee for the strength of the infusions. 



I took advantage of the clear weather this year to investigate the 

 action of solar light on the development of life in these infusions, being 

 prompted thereto by the interesting observations brought before the 

 Eoyal Society by Dr. Dowues and Mr. Blunt in 1877.' The sealed ends 

 of the flasks being broken off, they were infected, in part by the water of 

 an adjacent brook and in part by an infusion well charged with organisms. 

 Hung up in rows upon a board, half the flasks of each row were securely 

 shaded from the sun, the other half being exposed to the light. In some 

 cases, moreover, flasks were placed in a darkened room, within the house, 

 while their companions were exposed in the sunshine ontside. 



The clear result of these experiments, of which a considerable number 

 were made, is that by some constituent or constituents of the solar radia- 



' Proc. Itoy. Soc, December 6. 



