Observing Animals in Motion 221 



thus materially affect the erosion. With respect to this, 

 the experiments showed that the erosive action depended 

 much on the kind of powder used, but appeared to be 

 independent of the amount of sulphur, for the one which 

 produced the smallest effect had the largest proportion of 

 that mineral. The heat developed by the explosion appeared 

 to be the most important factor. To measure the amount 

 of erosion, the powder was placed in a steel vessel with a 

 very small vent, through which the products of explosion 

 had to escape, and their effects were measured by the 

 quantity of steel removed. Captain Noble described a 

 curious effect produced upon a screw in one experiment, 

 when a large charge about 24 pounds was fired, giving 

 a tension of about 43 tons. 



Sir H. Lefroy exhibited some samples of merino wool 

 from Tasmania, remarkable for its fineness, and for the high 

 price (1400 guineas) that had been paid for the sheep that 

 had produced it. 



June I5th, Siyth meeting. Mr. Galton exhibited an 

 instrument which he had made to verify the attitudes 

 of an animal in rapid motion. By tapping a stud, a slit on a 

 screen was made to move rapidly in front of an eyehole, 

 thus affording a momentary glance of an object. Thus the 

 ye (far more sensitive than any plate in a photographic 

 camera) could obtain a distinct image of the animal at an 

 instantaneous phase of its motion. He thought naturalists 

 would find the instrument useful in observing the habits of 

 birds and insects, and physicists for such things as plants in 

 rapid motion. 



Nov. gth, 3i8th meeting. Before the minutes (by an 

 inadvertency there was no meeting on Oct. 26th) a cutting 

 from the Times is inserted, recording the death, on July iQth, 

 of Professor F. M. Balf our, with his guide, Johann Petrus, of 

 Stalden, on the Aiguille Blanche de Peuteret. 1 



1 The letter is reprinted, accompanied by some further information, 

 in the Alpine Journal, vol. xi. pages 90-93 ; pages 101-103 giving an In 

 Memoriam notice. The first ascent of this dangerous peak was made 

 Aug. 28th, 1913 (Alpine Journal, vol. xxviii. pages 81, 82). 



