322 Mr Drummond's Apparatus for producing Intense Light. 



burner, of the best construction, and supplied with the finest 

 oil. The lime from chalk, and such as is known at the Lon- 

 don wharfs by the name of Flame-lime, * appears to be more 

 brilliant than any that has been tried. 



" The lime from the chalk, besides being the most brilliant, 

 is, in other respects, very convenient for use ; it admits of 

 being turned in the lathe, and thus any number of the small 

 focal balls, with slender stems attached to them, may be pre- 

 pared with the utmost facility. The surface of the ball, by 

 the continued action of the heat, appears to be kept nearly in 

 a state of fusion. It is gradually worn down, and in cooling 

 presents a semi-crystalline appearance."" -f" 



This method of producing an intense light, visible at a great 

 distance, was successfully applied, in October 1825, to the pur- 

 poses of the trigonometrical survey in Ireland. The lime-light 

 was exhibited by Mr Drummond on Slieve Snaght, the high- 

 est hill of Innishowen, about 2100 feet above the sea, and 15 

 miles north of Londonderry ; and it was distinctly seen from 

 the Divvis hill near Belfast, a distance of 66^ miles. Colonel 

 Colby proposes to employ this light to effect the observation 

 of Benlomond from Knock-Layd, in the north-east extremity 

 of Ireland, a distance of 95 miles, and of the Calton Hill, 

 Edinburgh, from Benlomond, and thus to measure the differ- 

 ence of longitude between the Edinburgh Observatory and that 

 of Dublin, which is nearly in the meridian of Knock-Layd. 



We cannot conclude this abstract without noticing the 

 strange oversight of Lieutenant Drummond in ascribing to 

 M. Fresnel the invention of the compound or built up lens, 

 which he could scarcely fail to know was invented by Dr 

 Brewster, and described by him in the Edinburgh Encyclo- 

 pedia ten years before M. Fresnel directed his attention to 

 the subject. 



* Well-burned Carrara marble, made into a paste and gradually dried,, 

 was found by Mr Drummond to be nearly equal to the Jlame-limc. 



t Mr Drummond found that the intense light discoloured a mixture of 

 chlorine and hydrogen, and produced an equally remarkable effect on chlo- 

 ride of silver. 



