/. Croll — Influence of the Gulf -stream. 157 



fifths. But it seems to me that this rule can hardly be very- 

 accurate, and that it would be desirable to find the mean ve- 

 locity by the use of a current metre, working in difi'erent parts of 

 the section. However, this element once determined, it is of course 

 only necessary to multiply the area of the section in feet, by the 

 mean velocity in feet for a given time, to ascertain the number of 

 cubic feet which flow past in that time, 



3rd. The proportion of sediment held in"suspension is ascertained 

 by collecting a certain measure of water (a quart bottle answers the 

 purpose very well), and then decanting and filtering it. If the 

 filter be carefully dried and weighed, before and after the experi- 

 ment, the difference gives the weight of mud from which the per 

 centage of grains to ounces of water can be obtained. We shall 

 now have sufficient data to determine how much solid matter passes 

 down the river in a given time at any flood. 



4th. Besides these observations, the rainfalFat different points of 

 the watershed of the river should be carefully registered. Thus 

 some correlation between the two could probably be ascertained, so 

 that from year to year an average rate of the wear and tear of the 

 surface of the land might be obtained. 



Many subjects of interest will naturally suggest themselves as we 

 proceed with these experiments, such as the variation of the 

 sediment after a long drought, and after a continued fall of rain. 



Of the above data, the most unsatisfactory are those relating to 

 the mean velocity of the stream at different heights. Perhaps some 

 of your readers may be able to furnish suggestions upon the best 

 mode of ascertaining this. 



Besides the mud actually held in suspension, it would be very 

 desirable to determine the rate at which the mud, sand, and gravel 

 which compose the bed of the river are propelled. Some suggestions 

 on the means of doing so would be very acceptable. 

 Stoeesay, Craven Arms, Salop, 

 February 5th, 1869. 



V. — On the Influence of the Gulf-stream. 

 By James Croll, of the Geological Survey of Scotland. 



THE modern method of determining the amount of heat effects in 

 absolute measure is no doubt destined to cast new light on all 

 questions connected with climate, as it has done and is still doino- in 

 every department of physics where energy under the form of heat is 

 the phenomenon under consideration. 



Owing to the complicated nature of the phenomena with which 

 the meteorologist has generally to deal, the application of this method 

 will very often be found practically impossible. The method, how- 

 ever, is particularly suitable to all questions regarding the direct 

 thermal effects of currents, whatever the nature of those currents 

 may happen to be. 



If the question, for example, is a^ked — "Is the heat conveyed 

 by the Gulf-stream suificient to affect to any great extent the 



