290 SGIENCK AY SHORT CHAPTERS. 



breakwater. The oil valves were opened, and immediately 

 the effect was manifest. The waves, which had before 

 'dashed with fury against the breakwater, assumed a rolling 

 motion and were quite crestless. Indeed, it was admitted 

 that the oil had rendered the entrance comparatively safe, 

 but the effect was not so abiding as could have been wished." 



As regards the want of duration there noted, I venture 

 to make a suggestion. 



Oils vary so greatly in their rate of outspreading over 

 water and the character of the film they form, that some 

 years ago Mr. Moffatt, of Glasgow, proposed to use these 

 differences as a test for the adulterations of one kind of oil 

 with other and cheaper kinds. 



I made a number of experiments verifying some of his 

 results. 



From these it is evident that the duration of the becalm- 

 ing effect will vary with different oils, and therefore further 

 experiments upon these difference should be made, in order 

 to select that kind which is the most effective, with due re- 

 gard, of course, to cost. 



The oil indicated by my experiments as combining per- 

 manency and cheapness, and altogether the most suitable 

 and attainable is the " dead oil " refuse of the gas-works. 

 This may be used in its crude and cheapest condition. 



ON THE SO-CALLED "CRATER NECKS" AND 

 "VOLCANIC BOMBS" OF IRELAND. 



A PAPEK READ AT THE GEOLOGISTS' ASSOCIATION, 

 DECEMBER 6, 1878. 



MR. HULL, " Physical Geography and Geology of Ire- 

 land," p. 68, under the head of "Volcanic Necks and 

 Basaltic Dykes," says that " although the actual craters 

 and cones of eruption have been swept from the surface 

 of the country by the ruthless hand of time, yet the old 

 ' ' necks" by which the volcanic mouths were connected 



