36 



SCJENCE. 



[Vol. VIII., No. 179 



la such an arid and hot climate, evaporation alone 

 would probably prolong the time of flooding for 

 hundreds of years : indeed, the time might be pro- 

 longed indefinitely, for the loss by evaporation might 

 ultimately be equal to ^e supply by inflow. We 

 have a case in point in Pyramid Lake, in Nevada, 

 into which the bold and rapid outlet of Lake Tahoe 

 (Truckee Eiver) perpetually flows without flooding it. 

 Of course, by increasing the dimensions of the Inlet 

 Canal, or augmenting the velocity of the inflowing 

 water, the computed time of flooding might be pro- 

 portionately shortened ; but, after all, the feeble 

 efforts of man are insignificant in relation to the 

 great hydraulic systems of nature. 



John LeConte. 

 Berkeley, Cal., June 29. 



A dissolving smoke-ring. 



The remarkable breaking-up of a smoke-ring from 

 a locomotive in Chicago was observed by me, a few 

 days since, in company with a mechanical engineer 

 of New York, whose estimate of size and height I 

 adopt. The ring rose to an elevation of about one 

 hundred and fifty feet, and attained a diameter of 

 twenty or twenty-five feet, as nearly as could be esti- 

 mated. It broke up suddenly with a rush of the 

 smoke along the line of the ring towai'd two centres ; 

 namely, the smoke of the south half coming together 

 in the centre of that half of the line, and the smoke 

 of the north half correspondingly to a centre in the 

 north. After these momentary and confused aggrega- 

 tions, all semblance of form disappeared. A vortex 

 ring is different from the theoretic planetary ring 

 breaking up into satelhtes, but aggregation of the 

 dissolving smoke-ring is suggestive. 



H. W. Parker. 

 Grinnell, lo. 



Surface tension and muscular contraction. 



I would offer as an attempt to explain the nature 

 of muscular contraction the hypothesis that the con- 

 traction is due to the phenomena of surface tension. 



By surface tension of a liquid is meant a peculiar- 

 ity presented by its surface, due to a difference in 

 state between the molecules in the surface and those 

 in the interior of the liquid. That there must be an 

 essential difference between the surface of a mass 

 and its interior follows from the fact that the molec- 

 ular forces acting on any particle within the mass 

 are equal in every direction, and so must balance 

 one another ; while the particles in the surface film, 

 having no particles above them, are acted on only 

 from below and at the sides, and so are constantly 

 drawn down against the mass : so that the liquid must 

 be under a definite surface tension. 



This surface film behaves as a perfectly elastic 

 membrane stretched in every direction by equal ten- 

 sions, and takes the form of smallest area consistent 

 with the conditions. This tendency of the film vo 

 become as small as possible is well illustrated by the 

 soap-bubble, which may be considered as a layer of 

 water with two surface films. So, when left to its 

 own molecular forces, a drop of liquid assumes that 

 form having the smallest superficies, with a given 

 content, which is the sphere. 



When a drop of liquid rests upon a surface which 

 it does not wet, it assumes the form of a sphere more 

 or less flattened out ; and the greater the surface 

 tension of the liquid forming the drop is, the more 



nearly does it approach the spherical form, and what- 

 ever alters its surface tension causes a corresponding 

 alteration in the form of the drop. 



Many substances, even in small quantity, exert a 

 considerable influence on the surface tension of 

 liquids. 



If a drop of water resting upon a greasy surface, 

 which it does not wet, be touched with a little 

 alcohol, its surface tension is diminished, and it 

 immediately spreads out over a larger area ; but, 

 when the alcohol evaporates, the surface tension of 

 the water is increased, and it again contracts into a 

 more globular form. 



Eemarkable changes in form are caused when a 

 globule of mercury is electrically polarized. In or- 

 ganic substances the surface tension increases with 

 the increase of certain elements entering into their 

 composition, and diminishes with the increase or 

 diminution of others ; e.g., in butyric acid and acetic 

 anhydride the increase of oxygen and diminution of 

 hydrogen increase the surface tension. 



Now, to see the bearing of this upon the contrac- 

 tion of a muscular fibre, it is necessary to remember 

 that the surface tension of a liquid may be changed 

 by a change in its composition, that the contracting 

 elements of a muscular fibre are the cells, and that 

 the composition of the cells is changed at the time of 

 a contraction. 



The cells are of an oblong shape extended in the 

 axis of contraction ;.and when contraction occurs the 

 cells grow shorter and thicker, just as an oblong 

 drop of water grows shorter and thicker when its 

 surface tension is increased. 



Now, a tendency to contraction must follow an in- 

 crease in the surface tension of the cell ; and that 

 there probably are changes in the surface tension of 

 the cell during contraction, follows from the fact that 

 there are chemical changes in the cell, more rapid 

 during contraction than rest. The changes occurring 

 in acting muscle may be identical with those in rest- 

 ing muscle ; but in resting muscle, restoration keeps 

 pace with destruction, while in contraction, destruc- 

 tion largely exceeds restoration : so any thing hasten- 

 ing the decompositions within the cell may cause con- 

 traction. 



Exhaustion is explained by the accumulation of 

 products of decomposition, since fatigue in muscles in 

 which circulation has ceased may be readily removed 

 by renewing the current of blood. 



This hypothesis may be thus summed up : the 

 active shortening of the fibre is due to an increase in 

 the surface tension of the substance of the cell, 

 caused by an increase in the proportional amount of 

 the products of decomposition. Equilibrium is re- 

 stored — after the stimulus which hastened the 

 chemical changes has ceased — by a part of the 

 products of decomposition finding their way into the 

 blood- current, and possibly by the remaining products 

 helping to build up the original compound. 



Elmer Starr, M.D. 

 Buffalo, N.Y., June 25. 



Trenton natural history society. 



So far as my own communications to the Trenton 

 natural history society are concerned, the report 

 thereof in Science (viii. No. 178) is a wilful misstate- 

 ment. As what I did state will soon be published, 

 it is unnecessary to enter into explanations. 



Chas. C. Abbott. M.D. 

 Trenton, N.J., July 2. 



