122 



SCIENCE 



[N. S. Vol. XLIX. No. 1257 



Tliursday Island measured and pliotograplied 

 by Saville-Kent were remeasured by Mayer 

 twenty-three years later. These results show 

 that large coral heads may increase as much as 

 two inches in diameter per year, while some 

 kinds do not grow beyond a certain specific size. 

 The average annual growth appears to be about 

 one inch, though in the Floridian reefs the rate 

 of increase is less. 



Mayer states that stream waters pouring out- 

 ward from forested volcanic shores are alka- 

 line and thus can not dissolve limestone by 

 reason of their " acidity." Thus the Murray- 

 Agassiz solution theory of the formation of 

 atolls is not supported. Holothurians are a 

 potent factor in dissolving the materials that 

 go to make reef limestones, which they swal- 

 low, and the effects of currents in scouring are 

 important factors tending to convert fringing 

 reefs into barrier reefs. 



The problem of the precipitation of CaCOj 

 in "the ocean and the possibility of its solution 

 there is discussed in the light of the latest evi- 

 dence, and the conclusion is reached that in 

 the shoal waters of the tropics, ocean-water 

 does not dissolve calcium caribonate, but that 

 the contrary process — precipitation by both in- 

 organic and organic (bacterial) agencies — is 

 taking place. Conditions in the deep sea, and 

 perhaps in the cold waters of high latitudes, 

 are different. 



, In the Murray Island reef sediments, 

 Vaughan states that the dominant rock makers 

 are (1) corals (34 to 42 per cent.) ; (2) coral- 

 line algag (32 to 42 per cent.) ; (3) molluscs (10 

 to 15 per cent.) ; f oraminifers (4 to 12 per cent.) 

 and alcyonarians. Other marine animals are 

 unimportant in their skeletal additions. 



Cary shows that, in the Tortugas area, the 

 gorgonians are also very important reef build- 

 ers and therefore great rook contributors, since 

 nearly 20 to 36 per cent, of their bodies consists 

 of calcareous spicules. As almost all of these 

 colonies die a violent death, and on the average 

 all those living within 30 feet of water are re- 

 placed in five years by other colonies, he cal- 

 culates that at least one ton of spicules or lime- 

 stone is added per year to each acre of reef 

 ground. In fact, when the gorgonians are 



common, they are more important as limestone 

 makers than are even the stony corals. 



Charles Sohuciiert 



SPECIAL ARTICLES 



A METHOD OF DEMONSTRATING THE 

 DIFFERENCE-TONES 



If a Eayleigh inductometer bridge be con- 

 nected up, and a telephone receiver 4 be in 

 series with the alternating e.m.f., the demon- 

 stration of the difference-tone is an exceed- 

 ingly simple matter. Let the bridge be bal- 

 anced for a high frequency F', say about 

 2,500; this tone will therefore not reach the 

 ears if the balancing receivers be of the double, 

 head-strap variety. ISTow whistle a scale into 

 the receiver A. Since the bridge is not bal- 

 anced for the new frequency, the whistle " gets 

 through " into the balancing receivers. But 

 one also hears another tone which slides down 

 as the whistle slides up the scale. If between 

 the balancing receiver and the bridge a good 

 amplifier be connected, then the balancing re- 

 ceiver may be a " loud-speaking receiver " 

 (such as are now used for announcing trains 

 in large stations, etc.) and the apparatus is 

 suitable for class demonstration. The great 

 advantage of this arrangement is that we are 

 not confined to any two fundamentals, as in 

 the case of forks. 



The phenomenon is unquestionably slightly 

 complicated by the action of one alternator on 

 the other, but I had not the time to see to 

 what extent the extra tone differs from F'—F". 



The writer offers the above as a lecture ex- 

 periment in physics and psychology, being 

 under the impression that it has not been 

 reported before. Paul F. Gaehr 



Wells College, 

 Aurora, N. Y. 



THE AMERICAN. ASSOCIATION FOR 

 THE ADVANCEMENT OF SCIENCE 



REPORT OF THE TREASURER FOR 1918 



In conformity with Article 15 of the constitu- 

 tion and by direction of the council, the treasurer 

 has the honor to submit the following report for 

 the period December 15, 1917, to December 16, 

 1918, both inclusive. 



