226 Boy al Irish Academy. 



from three to seven nights in each month. He stated, that when 

 he had undertaken this series of experiments, he had the following 

 objects in view — namely, to determine the mean amount of electric 

 intensity existing in this country, at the different hours of day and 

 night, and the periods of maxima and minima ; and, secondly, to 

 endeavour to trace the cause of this varying intensity to the influ- 

 ence of some of the recognised agents in nature, — such as the varia- 

 tions of atmospheric pressure ; the variations of temperature ; or 

 the varying quantity of vapour in our atmosphere. 



He was happy to announce, that he had not only determined the 

 mean monthly and annual force of electricity at the several hours 

 of the day and night, but also had succeeded in establishing its de- 

 pendence upon two, out of the three agents, with which he had 

 originally proposed to investigate its connexion. The two with 

 which he has established its connexion and proved its dependence 

 are, temperature, and the total quantity of moisture present in the 

 air, as shown by the dew-point. Indeed these two phsenomena, as 

 the author remarked, are referrible to each other, the temperature 

 producing evaporation, and the force of electricity at any period 

 being shown to be almost exactly proportional to the tension of the 

 vapour so produced. 



The hour of the first electric minimum was shown to be about 

 3 A.M., the electricity increasing with the temperature until 10 

 A.M., when a slight decrease occurred: the electric tension again 

 commences rising at about 11 a.m., and continues to increase until 

 about 2^^ 45"", p.m. — aU these movements being in exact proportion 

 to the elevation of the dew-point and temperature. At 3 p. m. the 

 dew-point and temperature begin gradually to lower, as does also 

 the electricity (but not so quickly); but from 5 to 7 p. m., the elec- 

 tric intensity rises, being acted upon and increased by the precipi- 

 tation of the evening dew, which has set free the latent electricity 

 of the condensed vapour, in conformity with the experiment of 

 Volta. Again, from 7 p. m., the electric intensity weakens rapidly, 

 and descends in common with the dew-point and temperature, until 

 they all reach their minimum about 3 a. m. 



Thus the patient investigation of this subject has laid bare the 

 cause of the varying diurnal intensity of the electric fluid, — showing 

 it to be the result of evaporation, which, besides its agency in carry- 

 ing the electric fluid from our earth to the upper regions of the air, 

 daily returns it to us by the conducting power of this vapour, in the 

 direct proportion of its quantity. 



Dr. Apjohn read a note by George J. Knox, Esq., " On the Oxi- 

 dating Power of Glass for Metals, and on the want of Transparency 

 in ancient Glass." 



" In a late work, which treats of the manufacture of glass, an 

 experiment of Guyton Morveau is mentioned, in which six per cent, 

 of copper filings having been mixed with pounded glass, and the 

 compound completely melted, it was found to have assumed a red 



