362 



PKOE. W. J. SOLLA.S ON THE MODE 0E [Aug. 1 895, 



Of several experiments which I am now making I venture on 

 this occasion to bring but one before the notice of the Society ; the 

 results obtained by it are so positive and striking that there can be 

 no reason for delaying their publication. 



A rectangular trough, measuring internally 6 cm. in width, 

 6 cm. in depth, and 30 cm. in length, was made of wood ; it was 

 closed at one end, and so constructed that by the removal of some 

 screws it would readily fall into halves along a median longitudinal 

 section. A barrier of wood 23 mm. in height and 20 mm. in 

 breadth extended completely across the trough at a distance of 

 115 mm. from the closed end (fig. 3, p. 364). 



The trough was placed in position for charging with cobbler's 

 wax — perhaps for the sake of brevity we may be allowed to call 

 this ' pitch ' — by raising it at the open end, so as to give it a tilt 

 of nearly 12°. 



The pitch, melted by boiling it in a ' glue-pot ' arrangement, 

 was then poured in up to the level 1 (fig. 1) ; it was allowed time 



Fig. 1. — The pitch '■glacier' at the commencement of the experiment. 



1, 2, 3=layers within the pitch having an uniform slope of 11° or 12°. 



4=original surface of the 'glacier.' The lines to the right of this 

 represent the contours of succeeding surfaces in later stages of 

 the experiment. 



to solidify and then covered with an even layer of crystals of sugar, 

 a substance which subsequent experience proved should be avoided 

 in these experiments. Fresh material was poured in till the level 2 

 was reached, and on solidification an uniform layer of sago was 

 spread over it. A third stratum of pitch was now added, and its 

 surface thickly dusted with powdered vermilion ; a last layer of 

 pitch poured over this rose to the edge of the closed end of the 

 trough on the one hand, and on the other just overbrimmed the 

 summit of the transverse barrier. "When the whole had cooled to 

 the temperature of the room, the trough was untilted, and set to 

 rest with its sole in a horizontal position. The upper surface of 

 the wedge of pitch was consequently inclined at an angle of about 

 12°. Horizontal lines were now ruled across the upper surface of 

 the ' glacier ' at distances of 30, 60, 90, and 115 mm. from its highest 



