1885.] The Upper Partial Tones of a Pianoforte String. 83 



tion of iodine in carbon disnlphide. It differs from the curve due to 

 the empty cell only in the visible and shortest wave-length portion of 

 the invisible spectrum, as might be expected. We have also examined 

 plain carbon disnlphide and carbon tetrachloride, but have found 

 only small traces of absorption with these liquids. 



We have found that alum solution gives a curve which differs but 

 little from No. XI in the least refrangible part of the spectrum ; the 

 alum seems to intensify the absorptive power of the water in which it 

 is dissolved. It has been so often stated that an alum solution cnts 

 off all rays of low refrangibility (or as it is incorrectly and commonly 

 said, all "heat rays") that we were not prepared for the compara- 

 tively small effect that it produces. It may be said that, roughly, 

 one thickness of a saturated solution of alum in water is equivalent to 

 a double thickness of water, and not more. Judging by the thermo- 

 grams, even this wonld be an exaggeration of the truth ; bnt the use 

 of glass in the cells, prisms, and lenses diminishes the effect as found 

 when the total radiation is taken directly. 



We may add that dyes seem only to absorb in the visible spectrum, 

 and to have but little, if any, action in the invisible regions. 



The positions which we assign to the maxima of energy in the 

 different absorption spectra of glasses do not agree with those that 

 have been published ; but as ours are the result, not of one set of 

 experiments, but, in some cases, of dozens, we feel fairly confident 

 as to their correctness. 



IV. " Observations on the Upper Partial Tones of a Pianoforte 

 String, struck at one-eighth of its Length." By Alfred 

 James Hipkixs (of John Broadwood and Sons, London). 

 Communicated by Alexander J. Ellis, F.R.S. Received 

 January 7, 1885. 



This is a postscript to my paper on the harmonics of such a string, 

 read on the 20th of November, 1884. According to Professor 

 Helmholtz's theories, the tone of a struck string is compounded of a 

 number of simple partial tones, with the ratios of their frequencies as 

 1, 2, 3, 4, &c. The harmonics are themselves also compound tones of 

 which the primes or lowest partials are the partials of the original 

 tone. These are produced on damping the other partials by touching 

 them at a node. Now, in my former paper, I showed that by so 

 touching 1 could bring out twenty different harmonics of the string, 

 and among these the 8th and 16th. Young's law, however, makes an 

 harmonic impossible to produce, if its node is the point struck. Hence 

 the string being struck at one-eighth of its length, no 8th or 16th 



