168 PLYMOUTH INSTITUTION. 



may be repeated several times in succession. One in Woodstock 

 Park repeats 17 syllables by day and 20 by night, there is a very 

 tine echo beneath the suspension bridge over the Menai Straits, the 

 effects of which were described by the Lecturer at some length ; 

 he also made some remarks on the importance of attending to the 

 nature of echos in the construction of large buildings, such as 

 churches, cathedrals, theatres, &c., where music and speaking aloud 

 were of frequent occurrence. 



Liquids being elastic and compressible are also adapted to the 

 propagation of sound ; Franklin having plunged his head below water 

 caused a person to strike two stones together, beneath the surface, 

 and, at a distance of more than half a mile, he heard the sound dis- 

 tinctly. Some careful and exact experiments were made in the lake 

 of Geneva, to determine the velocity of sound in water. 



In the course of these experiments M. Colladin was led to remark 

 some curious particulars respecting the nature, intensity, and duration 

 of sounds propagated by water. He observed that the sound of a 

 bell struck under water, when heard at a distance, bore no resem- 

 blance to its sound in air instead of a continued sound, a short, 

 sharp sound is heard, like that of two knife blades struck together. 

 The effect of hearing such a short dry sound, at a distance of many 

 miles from its origin, he compares to that of seeing very distant objects 

 sharply denned, by a telescope. When tried at different distances 

 it preserved this character, varying only in intensity, so as to render 

 it impossible to distinguish whether the sound arose from a violent 

 blow at a great distance, or a gentle one near at hand. In the air 

 the contrary takes place, the shock of the first impulse only is heard 

 in the immediate neighbourhood of the bell, while the continued 

 musical sound is the only one that is heard at a distance. 



Another very curious observation of M. Colladin is that relative 

 to the effect of interposed obstacles. Sounds in air spread around 

 obstacles with great facility, and with very little diminution of inten- 

 sity, but in water this is far from being the case. 



When a cylinder or hearing pipe was plunged into the water, 

 at a place screened from communication with the bell, by a wall 

 running out from the shore of which the top rose above water, a very 

 remarkable diminution of the sound was observed when compared 

 with that at a point near the former in direct communication with 

 the bell. 



The Lecturer next detailed some instances and experiments to 

 prove that elastic solids, such as glass, steel, &c. are as well adapted 

 to the conveyance of sound as liquids, and perhaps better than they 



