520 The British Association. [October, 
with a clear knowledge of the most essential conditions 
required in a perfect brake. 
The Rev. Robert Harley, F.R.S., read a paper “ On the 
Stanhope ‘ Demonstrator,’ or Logical Machine.” The au- 
thor stated that towards the close of the last century a 
logical instrument was constructed by Charles, third Earl 
Stanhope. The present Earl found the instrument and some 
fragmentary papers on Logic among the relics of his scien- 
tific ancestors, and, at the suggestion of Mr. Spottiswoode, 
placed them in the hands of Mr. Harley, who has made a 
careful study of them. Earl Stanhope (born 1753, died 
1815) is known to Science chiefly by his printing-press, mi- 
croscopic lens, arithmetical machine, monochord, and steam- 
boat ; but of his logical speculations, which occupied his 
thoughts for thirty years, and of his curious contrivance for 
working logical problems, called by him the “ Demonstrator,” 
nothing has been known. Mr. Harley noticed that Stan- 
hope anticipated George Bentham, Sir William Hamilton, 
George Boole, and others, in his quantification of the predi- 
cate, and notably De Morgan’s rule for the numerically 
definite syllogism. Stanhope stated the rule as applicable 
to all syllogistic reasoning, and he constructed his “ Demon- 
strator” for the mechanical working of the rule. It does 
not seem equal to very difficult and complicated questions, 
nor nearly so powerful as Prof. Jevons’s logical machine, 
which before the discovery of the “Demonstrator” was 
supposed to be the first invention in this direction. 
Dr. Janssen described his method of Solar Photography, 
and read a paper “ On Total Eclipses.” 
Mr. E. J, Hardman read a paper “ On Lead and Platinised 
Lead as a Substitute for Carbon and Platinised Silver in 
Leclanche, Bichromate, and Smee’s Batteries.” 
Mr. W. J. Millar described a new Receiver for Microphone. 
Mr. Mattieu Williams read a paper “ On an Experimental 
Verification of the Velocity of Transmission of Radiant 
Heat.” 
The “ Report of the Committee on Atmospheric Electri- 
city ” was read by Prof. Forbes. Three electrometers have 
been given: one to Surgeon-Major Johnson, in India; the 
second to Mr, Michie Smith, in India ; and the third to Dr. 
Grabham, in Madeira. Surgeon-Major Johnson was engaged 
in the frontier war in India ; and Dr. Grabham has hitherto 
been too much occupied to make observations ; while 
Mr. Michie Smith has not yet had time to furnish any ; 
