45 be ~ Lieut. Drummond’s Station Light, Sc. 
to this me thod on some occasions that occurred in the Trigo- 
nometrical Survey of England, where, from peculiar local cir- 
cumstances, much difficulty was experienced in discerning the 
usual signals. 
Even as a temporary expedient, and under a rude form, viz. 
that of placing tin plates at the station to be observed in such 
a manner that the sun’s reflection should be thrown towards 
the observer at a particular time, the most essential service 
was derived from its use; and the consequence was, the inven- 
tion of a more perfect instrument, of which a description is 
given, accompanied with a drawing. 
The second method consists in the exhibition of a very bril- 
liant light at night.. At the commencement of the Survey of 
England, General Roy had recourse, on several occasions, 
and especially in carrying his triangles across the Channel, to 
the use of Bengal and white lights; for these, parabolic reflec- 
tors illuminated by Argand lamps were afterwards substituted 
as more convenient; but from want of power they appear in 
turn to have gradually fallen into disuse. With a view to 
remedy this defect, a series of experiments was undertaken by 
Mr. Drummond, the result of which, was the production of a 
very intense light, varying between 60 and 90 times that of 
the brightest part of the flame ofan Argand lamp. 
This brilliant light is obtained from a small ball of lime 
about 3-Sths of an inch diameter, placed in the focus of the re- 
flector, and exposed to a very intense heat by means of a sim- 
ple apparatus, of which a description is given, with drawings. 
A jet of oxygen gas directed through the flame of alcohol is 
employed as the source of heat. Zirconia, magnesia, and 
oxide of zinc were also tried; but the light emanating from 
them was much inferior to that from lime. Besides being 
easily procured, the lime admits of being turned in the lathe, 
so that any number of the small focal balls may be readily 
obtained, uniform in size, and perfect in figure. ‘lhe chemical 
agency of this light is remarkable, causing the combination 
of chlorine and hydrogen, and blackening chloride of silver. 
Its application to the very important purpose of illuminating 
light-houses is suggested, especially in those situations where 
the lights are the first that are made by vessels arriving from 
distant voyages. 
Both the methods now described, for accelerating geodesic 
operations, were resorted to with much success during the 
last season in Ireland; and on one occasion, where every at~ 
tempt~to discern a distant, station had failed, the observations 
were effected by their means, the heliostat being seen during the 
day, when the outline of the-hill ceased to be visible, and the 
light at night being seen with the naked eye, and appearing 
much brighter and larger at the distance of 66 miles, than a 
parabolic 
