I 



PLYMOUTH INSTITUTION. 265 



March 26th. — Reports on Science. 



Circumstances having prevented the delivery of the Scientific 

 Reports, at the commencement of the Season, they w^ere laid 

 before the Society this evening. Mr. Harris confined his report 

 chiefly to Electro Chemical Science, and explained some of the 

 most remarkable additions v^rhich had been made to it by the re-^ 

 searches of Faraday and others : after explaining some of the. 

 elementary principles of Electro Magnetism, he traced it up to 

 its present state, and exhibited to the Society the Apparatus em- 

 ployed for the production of the electrical spark from copper 

 wires, surrounding a mass of iron, operated upon by magnetic 

 induction alone ; after which — 



Mr. Prideaux commenced by stating the impossibility of com- 

 pressing for the occasion, any thing like a report of all the recent 

 discoveries in a science so multifarious as Chemistry, it would 

 therefore be confined to such of them as were of some general in- 

 terest; leaving the enquiry into any of the more confined ones 

 for the discussion. The reporter then read a list of them,., which 

 we cannot pretend to repeat ; and can only observe upon it, that 

 the technical language of Chemistry sounded like no tongue that 

 ever was uttered before, and strangely illustrated the effect of 

 compounding names from two or three dead languages together. 



The first subject reported on was, a mode of measuring light, 

 which was illustrated by reference to the most successful methods 

 previously in use. These were Count Rumford's, by the com- 

 parative intensity of shadows ; and Sir J. Leslie's, by the differ- 

 ential thermometer. The difficulties attending the first of these 

 were shewn in the case of lights differing greatly in intensity, 

 and still more in that of differently coloured lights. Sir J. 

 Leslie's instrument was stated to be differently affected by lights 

 of equal intensity, when of different temperatures, and to indi- 

 cate no light at all from the moon. 



By the new instrument, the invention of Mr. Talbot, M.P., 

 some of these difficulties were surmounted. It consists of two discs 

 of card or any other thin material, divided into 24 equal parts, 

 and alternate divisions cut out, like a spoke wheel; these 

 being set on the axle of a multiplying wheel, and fixed together 

 so that the spokes of one coincided with those of the other : on 

 being put into rapid motion intercepted, of course, half the rays 

 of a lamp placed behind. When the spokes of one were placed 

 against the intervals of the other, no light could pass, and of 



