Sir John Lubbock’s Address. 3538 
construction had vastly improved. The Hddystone lighthouse, 
for instance, was built by Smeaton in 1759; but for forty years 
its light consisted in a row of tallow candles stuck in a hoop. 
The Argand lamp was the first great improvement, followed by 
gas, and in 1863 by the electric light. 
Just as light was long supposed to be due to the emission of 
material particles, so heat was regarded as a material, though 
ethereal, substance, which was added to bodies when their 
temperature was raised. 
Davy’s celebrated experiment of melting two pieces of ice 
by rubbing them against one another in the exhausted re- 
ceiver of an air-pump had convinced him that the cause of 
heat was the motion of the invisible particles of bodies, as had 
been long before suggested by Newton, Boyle and Hooke. 
Rumford and Young also advocated the same view. Never- 
theless, the general opinion, even until the middle of the present 
century, was that heat was due to the presence of a subtle fluid 
known as “calorie,” a theory which is now entirely abandoned. 
Melloni, by the use of the electric pile, vastly increased our 
knowledge of the phenomena of radiant heat. His researches 
Were confined to the solid and liquid forms of matter. Tyn- 
dall studied the gases in this respect, showing that differences 
greater than those established by Melloni existed between gases 
and vapors, both as regards the absorption and radiation of 
eat, e proved, moreover, that the aqueous vapor o 
heat and gaseous matter stood their ground. | ; 
Tne determination of the mechanical equivalent of heat is 
