September 4, 1896.] 



SCIENCE. 



299 



ameter. The axis of the wire of a ring is in 

 a plane ; in other words, the rings are flat. 

 Each of these rings has soldered to it a thin 

 wire along a diamter and raised above the 

 plane of the ring. On this wire is cemented 

 a platform of thin metal. These rings are 

 highly polished and are chemically clean. 



On loading one of these floating rings, by 

 gradually adding weights on its platform, 

 the ring sinks deeper and deeper below the 

 general surface of the water, till, finally, it 

 breaks through the depresssed surface. On 

 the form of this depressed surface (which I 

 have plotted) depends the amount of weight 

 per centimeter of circumference of the ring, 

 required for the ring to break through the 

 surface of the water. This weight, in the 

 cases of the rings mentioned, is, on the 

 average, 0.155 grams per centimeter, or 

 about double the surface tension of water ; 

 because tangents to the depressed surface 

 of the water, at the point w^here the rupture 

 occurs, are vertical. 



In the present stage of the research I am 

 inclined to hold the opinion that the flota- 

 tion of metals and of glass depends on a 

 film of air which is condensed on their sur- 

 faces. The following experiments seem to 

 sustain this opinion. If a ring made of 

 platinum wire ^ millimeter thick, which 

 readily floats on water, is heated to 

 redness and as soon as cold is placed on 

 water it sinks. Also, when withdrawn 

 from the water and wiped dry it again sinks 

 when placed on the water; but after the 

 same dried ring remains about a quarter of 

 an hour exposed to the air then it will float. 

 If the platinum ring, after having been 

 heated to redness, remains in the air about 

 a half hour and then is placed on the water 

 it floats. 



Glass behaves in a similar manner to 

 platinum. If a rod of glass, recently drawn 

 out in a spirit flame and just cold, is placed 

 on water it sinks. After a freshly made 

 rod has remained exposed to the air about 



a quarter of an hour it will float. If a 

 recently made glass rod which has just sunk 

 in water be withdrawn, wiped dry and ex- 

 posed to the air for a quarter of a hour, it 

 will float. The glass rods used in these ex- 

 periments are one millimeter thick and four 

 to five centimeters long. 



Under certain conditions the ratio of the 

 weights required to make a platinum ring 

 break through the surface of water and 

 through the surface of another liquid is the 

 ratio of the surface tension of water and 

 that of the liquid. This ratio is 1 : 1.09 in 

 the case of water and a solution of chloride 

 of sodium of density 1.2. Taking .077 as the 

 surface tension of water we have 1 : 1.09 = 

 .077 : .0839. Platinum is used for such ex- 

 periments because it is chemically inert to 

 nearly all liquids. 



Under certain conditions the ration of 

 the weights required to make a platinum 

 ring bread through the surface of water and 

 through the surface of another liquid is the 

 ratio of the surface tension of water and 

 that of the liquid. This ratio is 1 : 1.09 in 

 the case of water and a solution of chloride 

 of sodium of density 1.2. Taking .077 as the 

 surface tension of water we have 1 : 1.09= 

 .077 : .0849. Platinum is used for such ex- 

 periments because it is not oxidizable and 

 is chemically inert to nearly all liquids. 



The relation that the experiments men- 

 tioned in this article have to the surface 

 tension of water and other liquids, and to the 

 change of surface tension on the exposure 

 of a liquid to the air, will be discussed in a 

 paper containing a fuller account of facts 

 and theory than can be given in this notice. 

 Alfred M. Mayer. 



Maple WOOD, N. J., August 21, 1896. 



A GALL-MAKING COCCID IN A3IERICA. 



The numerous and extraordinary galls 



formed by Coccidge in Australia have long 



excited the interest of entomologists, but so 



far no gall-making coccid has been de- 



