188 
POPULAR SCIENCE REVIEW. 
observed northwards, inverse if southwards. It is in the same direction as a 
current would take to produce terrestrial magnetism. The rotation, if due 
to magnetism, should not be detected in a line perpendicular to the dip 
needle : by experiment this is found to be the case. 
The author of the memoir has already contributed valuable researches to 
the Comptes Hendus of the Academy on measuring the rotatory power of 
certain gase3, especially of air. These have been noted in this Summary ; 
and so has the observation of the power of terrestrial magnetism in rotating a 
ray passing through carbon bisulphide. By combining these with the facts 
above stated, M. Becquerel shows in conclusion, (1.) The existence of a 
variable angle between the sun’s plane and that of atmospheric polarization 
for the same point ; (2.) The periodic diurnal variation of this angle, closely 
connected with change of illumination ; (3.) The evidence of a magnetic 
influence of the earth on the atmosphere, producing a small but definite 
deviation in the plane of polarization. 
The History of Musical Pitch was given in detail by Mr. Alex. J. Ellis 
before the Society of Arts on March 3rd, the paper beng in some sense 
supplementary to a former communication on May 22nd, 1877, to which a 
Society’s silver medal was awarded. It had been objected to the former 
paper that the instrument used for measuring pitch, namely, Appunn’s Reed 
Tonometer, was hardly trustworthy, and that the results thus obtained were 
probably incorrect. M. Randolph Koenig especially wrote in this sense to 
the Monde of June 19th, 1877. ‘ A strange and unexpected attack,’ he 
writes, ‘ has been made in England on the accuracy of the French official 
Diapason. Mr. Ellis, having found that the notes of a Tonometer composed 
of sixty-five harmonium reeds did not agree with it, has thought fit to 
declare before the Society of Arts that the normal A does not give 870 
simple vibrations but 878. Mr. Ellis having, moreover, found that tuning- 
forks of my manufacture were accurately in tune with the French A, did not 
hesitate to affirm that all these instruments, including my large Tonometer, 
were necessarily false.’ He then quoted a letter from Helmholtz showing 
the inaccuracy of Appunn’s standard, and intimates, with some w r armth, that 
Mr. Ellis had neglected to verify his test instrument before using it. The 
writer of the present notice had already drawn the attention of the Musical 
Association to the same defect at a meeting on Nov. 6th, 1876. It was 
afterwards shown by Lord Rayleigh that the error was due to the natural 
influence of the reeds on one another when in a state of vigorous vibration. 
Mr. Ellis, in the present paper, frankly admits the charge, saying, ‘What 
the cause of this “ drawing ” of the beats may be has not yet been investi- 
gated.’ (This is incorrect.) ‘ Its direction and amount was, I believe, 
entirely unknown previously. I feel that I owe an apology to Herr Koenig 
for having been unfortunately misled by the unknown error of Appunn’s 
instrument to attribute that error to him. Besides this acoustical acceleration 
of the beats,’ he continues, ‘ there remain two other drawbacks to Appunn’s 
Tonometers: First, they do not retain their pitch with accuracy, and 
secondly, their variation with temperature is unknown. Hence they are 
not, as I had hoped, instruments of scientific precision, though admirable for 
all purposes of lecture illustrations.’ 
The remainder of the paper, being mainly concerned with historical 
