Proceedings of the Royal Society of Edlnhurgh. 19S 
LITERAIIY CLASS. 
Henry Mackenzie, Esq. President. Thomas Thomson, Esq. Secretary. 
Counsellors from the Literary Class. 
Professor Dunbar. Reverend Dr .lamiesori. 
Reverend Mr Alison. Reverend John Thomson. 
Lord Reston. Reverend Dr Brunton. 
J)ec. 3. — Professor Playfair read a paper on the Slide of 
Alpnach. This slide was erected by M. Rupp, in 1812, for 
the purpose of bringing down to the Lake of Lucerne the fine 
pine trees which grow upon Mount Pilatus. The wood was pur- 
chased by a company for L. 3000, and L. 9000 were expended in 
forming the slide. The length of the slide is about 44,000 Eng- 
lish feet, or about eight miles and two furlongs, and tlie differ- 
ence of level of its two extremities is about 2600 feet. It is a 
wooden trough, about five feet broad and four deep, the bot- 
tom of which consists of three trees, the middle one being a 
little hollowed, and small rills of water are conducted into iL 
for the purpose of diminishing the friction. The declivity, at 
its commencement, is about 22|°, and Mr Playfair calculated, 
that a heavy body, not retarded by friction, would describe the 
whole length of the trough in 66". The large pines, with their 
branches and boughs cut off, are placed in the slide, and de- 
scending by their own gravity, they acquire such an impetus 
by their descent through the first part of the slide, that they 
perform their journey of eight miles and a quarter in the short 
space of six minutes, and, under favourable circumstances, that 
is, in wet weather, in three minutes. Only one tree descends 
at a time, but by means of signals placed along the slide, 
another tree is launched as soon as its predecessor has plunged 
into the lake. Sometimes the moving trees spring or bolt out of 
the trough, and when this happens, they have been known to 
cut through trees in the neighbourhood as if it had been done , 
by an axe. When the trees reach the lake they are formed into 
rafts, and floated down the Reuss into the Rhine. The very 
singular phenomena described in Mr Playfair’s paper, arise from 
tlie diminution of friction, in consequence of an increase of ve- 
locity, and may be regarded as an experimental confirmation^; 
on a large scale, of the ingenious views of Coulomb, who had 
the merit of discovering this remarkable property of friction. 
Dec. 17' — Mr Fraser Tytler communicated to the Society 
VOL. I. NO. I. JUNE 1819. N 
