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readily washed away. In the Collotype, the picture is left on a 

 thick plate of glass, the gelatine is covered with a greasy ink by 

 means of a roller, and the impression is taken in a press. In the 

 Woodburytype the picture, after having had the soluble parts 

 removed by water, is pressed with great force upon a block of type- 

 metal, and the impression remains on the metal without injury to 

 the gelatine sheet. The metal block is then printed from by the 

 ordinaiy typographic method. A sheet of gelatine about as large 

 as a carte de visite was exhibited, which had been subjected to 

 a pressure of 48 tons. 



TUESDAY, APEIL 6th. 



Professor P. M. Duncan, M.B., F.E.S., F.G.S.. &c., gave a 

 Lecture on "Old and New Views concerning the Earth." 



The problem respecting the shape and size of the earth was 

 attacked by the earliest philosophers. The Ohaldaeans calculated 

 eclipses, and thus showed that they must have devoted much time 

 to the observation of the heavenly bodies. They noticed that the 

 hoiizon, as seen from any point of view, was circular, and they then 

 concluded that the earth was globular. Anaximander also advocated 

 its globular shape, and maintained that it rotated on an axis. 

 Advances in astronomy were made by Ptolemy, Pythagoras, and 

 Hipparchus. The Arabs attempted to measure the earth by a base 

 line, on one of the plains of Mesopotamia, and they came to the 

 conclusion that a degree was equal to about 56 miles. The 

 advocates of the spherical shape of the earth were ridiculed by 

 opponents, who insisted that men living at the antipodes would 

 stand head downwards, and would, therefore, be subject to headache 

 and apoplexy. Copernicus declared that the earth was one of a 

 series of bodies revolving round the sun ; and Bruno further asserted 

 that the stars are suns. The fact that a pendulum oscillates in 

 equal times was first observed by Galileo ; and it was by means of 

 experiments with the pendulum, that the elliptical figure of the 

 earth was discovered by Newton. The measure of an arc of the 



