160 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



antennoB vibrate with equal intensity, he has placed the axis 

 of his body in the direction of the sound. Experiments under 

 the microscope show that the mosquito can thus detect to 

 within five degrees the position of the sonorous centre. 



To accomplish the above would be to arrive at a new 

 method of analysis of sounds, and to give a complete experi- 

 mental confirmation of Fourier's theorem. This Professor 

 Mayer has succeeded in doing, as follows: A membrane is 

 placed near the sonorous body. Attached to a point of this 

 membrane are several fibres from a silk-worm cocoon. Each 

 of these leads to a tuning-fork. Now, it is known that a 

 tuning-fork can only give a simple sound, that is, a sound 

 having only one pitch. Hence, if any of the sounds which 

 are given by these forks exist in the sounds given by the so- 

 norous body, the forks giving these sounds, and only these, 

 will vibrate. Professor Mayer showed this by placing on 

 the prongs of the forks small pieces of wax. This system of 

 analysis is found to be so delicate that if the fork is thrown 

 out of tune by the weight of the piece of wax, so that it Avill 

 give one beat in eight seconds with the sound which it had 

 before it was loaded, it will thus detect this difference in the 

 pitch. According to Weber, of Germany, the most accom- 

 plished musical ear can detect a ditference of pitch in two 

 notes whose ratio of vibration is as 1000 to 1001 ; but by this 

 method a difference of pitch can be detected in two notes 

 w^here the ratio of vibration is 4000 to 4001. 



Professor Mayer then gave an account of experiments by 

 which he has partly succeeded in measuring the relative in- 

 tensity of sounds by the quan4,ity of heat that sounds give 

 when the bodies producing them are caused to send their vi- 

 brations into India rubber. The rubber is in the form of a 

 very thin sheet, stretched between the prongs of a fork, and 

 inclosed on the sides by a thermo-battery. Professor Mayer 

 is still conducting researches in this direction. Unless we 

 can measure the intensity of sounds, there is no science of 

 acoustics. Last year Professor Mayer made an initial step 

 in that direction, by measuring with great accuracy the rela- 

 tive intensity of sounds of the same pitch. But to measure 

 the relative intensity of sounds of a different pitch is a much 

 more difficult matter, and has not yet been accomplished. 

 Professor Mayer, however, hopes to succeed in this by con- 



