14b' Prof. C. V. Raman and Mr. Ashutosh Dey on 



photographs. In a recent paper* Mr. A, Mallock has 

 attempted to develop a mathematical theory of the formation 

 ol the air-cavity in the wake of the sphere, and he has also 

 discussed the part played by it in the production of the 

 characteristic sound accompanying the splash. Mr. Mallock' s 

 observations of the sounds of splashes were made with the 

 unaided ear, and are thus of a subjective and qualitative 

 character. Further investigation with instrumental aid is 

 obviously desirable f . 



The present communication is accompanied by some 

 photographic records of the sounds of splashes which the 

 authors have secured, showing the transition between the 

 " smooth " or " sheath " splash and the " rough " or 

 "basket"" splash, depending on the condition of the surface 

 of the impinging sphere. A brief description of the in- 

 strument with which the sound records were secured may 

 b ■>. of interest, as it has proved very convenient and easy to 

 construct, and also sufficiently sensitive. The design of the 

 instrument is due to Dr. P. H. Edwards J, who gave a 

 sketch of it in a personal communication to one of the 

 authors. The essential features of the apparatus are shown 

 in the diagrams (a) and (b). The sound-waves enter a horn 

 at the end of: which a mica disk is fixed. To the centre of this 

 disk is firmly fixed a steel spring which projects normally 

 from the disk. This spring presses upon a fine steel needle 

 resting on supports, and when the mica disk vibrates to and 

 fro, the movement of the spring causes the needle to roll 

 forward and backward on its supports. By means of the 

 screw shown in (a), the pressure of the spring on the needle 

 can be suitably regulated. To ensure the needle always 

 remaining parallel to itself, the supporting block is made 

 slightly curved to a cylindrical shape and cut away at the 

 centre as shown in (b). The angular movement of the 

 needle caused by its rolling is greatly magnified and optically 

 recorded on the moving photographic plate with the aid of a 



* Proc. Roy. Soc. vol. xcv., November 1918. Mr. Mallock quotes 

 only the Phil. Trans, paper of 1897, and was apparently unaware of 

 TVorthington's later work. 



t An interesting fact which may be mentioned in this connexion and 

 which requires investigation, is that the splash of a liquid drop is prac- 

 tically soundless unless the height of fall exceeds a certain minimum. 

 This effect appears to be connected with the change in the character of 

 the splash with increasing heights of fall noticed by AVorthington. 



} Dr. Edwards used an instrument of the type mentioned in the course 

 of some recent woik at the Bureau of Standards at Washington, the 

 results of which work still await publication. 



