546 Progress in Science. [October, 



the movement of which was determined by the principal watershed of the 

 Lake district. . 



Mr. j. F. Campbell has described the Glacial phenomena of the Hebrides. 

 Various ice-marks were noticed, which all seemed to come from the north and 

 west, also numerous perched blocks. On the whole, the author was inclined 

 to think that the last Glacial period was marine, and that heavy ice came in 

 from the ocean, the local conditions being like those of Labrador. He regarded 

 most of the Lake-basins of the Hebrides as formed by ice-action, and considered 

 that the ice by which those islands were glaciated came from Greenland. 

 Mr. James Geikie has also described the Glacial phenomena of Long Island, 

 or Outer Hebrides. The lakes of the mountain district he regarded as all 

 produced by glacial erosion. 



The Duke of Argyll has discussed the formation of six Lake-basins in 

 Argyllshire, five of which he considers could not have been due to glacial 

 action. 



The glaciation of the British Isles has received of late a good deal of atten- 

 tion, and the presence of sheets or fields of ice covering vast areas has been 

 invoked in order to account for the phenomena observable in different parts of 

 the Kingdom. Mr. R. H. Tiddeman, describing the glacial phenomena of 

 North Lancashire, and the adjacent parts of Yorkshire and Westmoreland, as 

 bearing testimony to a widespread and almost universal glaciation in the 

 district, brings forward evidence to show that they were produced by an ice- 

 sheet. While, however, the drainage of the district is to the south-west, the 

 general movement of the ice over it appears to have been to the south or south- 

 south-east, across deep valleys, and over hills of considerable elevation. This 

 he explains by the scratches on the rocks, the direction and method of trans- 

 port of the Till, its materials, and their arrangement along lines coinciding 

 with the scratches, as well as by the superficial disturbances of the rocks. To 

 account for the direction of the ice-sheet, which under ordinary circumstances 

 would be working down from the watershed to the sea in the direction of the 

 main valleys, Mr. Tiddeman considers that there must have been a great 

 barrier, along what is now the seaside plain, to dam up the mouths of these 

 valleys to a great height, and prevent their discharge of ice to the south-west. 

 Evidence of such a barrier exists in the traces of a great stream of ice coming from 

 the Lake district and bearing with it rock specimens of that country. This barrier 

 he concludes was but the line of junction of the ice of the Pennine chain with 

 that from the Lake district, and to the eye they must have presented only the 

 appearance of one great sea of ice. These observations, which Mr. Tiddeman 

 communicated to the Geological Society of London, are illustrated by a 

 coloured map upon which the physical features of the country are depicted 

 and the direction of the ice-scratches shown. 



PHYSICS. 

 Microscopy. — The most powerful spectroscope yet constructed has been pre- 

 sented to the University of Oxford by Mr. J. P. Gassiot. The great dispersive 

 power of the instrument is obtained by a battery of six compound prisms 

 3 inches high by 2 inches wide. The light, after passing through the upper 

 half of these prisms, is reflected back through the lower half, the light in its 

 course through the prisms having to pass through more than 4 feet of glass 

 before it reaches the eye of the observer. The telescopes are of 18 inches 

 focal length, and the object-glasses if inches in diameter. The prisms are 

 provided with the automatic arrangement for keeping them at the minimum 

 angle of deviation for any ray under examination. It is intended that all the 

 measuring of the spectra should be done by means of a micrometer eye-piece 

 placed in the telescope ; but for the purpose of readily finding any line in the 

 spectrum, the prisms are provided with a vernier which moves round a cir- 

 cular arc ; the divisions are on an alloy of palladium with silver. There is a 

 contrivance for setting the train of prisms in motion, the milled head which 

 moves the prisms being close to the eye-piece of the telescope, and thus com- 

 pletely under the command of the observer. The weight of the instrument is 

 rather more than 140 lbs. 



