250 



SCIENCE. 



[Vol. I., No. 9. 



of concavity of the film." The most simple and sat- 

 isfactory proofs of the relative efficiency, as well as 

 the direction, of the resultant of these capillary forces, 

 are to be found in the well-known contrary move- 

 ments of small columns of water and of mercury, 

 when introduced into conical capillary glass tubes 

 placed horizontally. In these cases it is evident, that 

 the effective forces are iuversely as the radii of curva- 

 ture of the terminal meuiscuses, and are directed 

 toward their respectix'e centres of concavity. 



He maintains, that, if the capillary forces were di- 

 rected toward the centre of concavity of the film, 

 " the tendency of a column of water raised between 

 two floating bodies by surface-tension would be to lift 

 those bodies : similarly, a column of liquid sustained 

 in a fine tube would tend to lift the tube." Simple 

 mechanical considerations are sufficient to show that 

 he is mistaken in supposing that such a residt would 

 follow. Indeed, it is obvious tliat the elastic reaction 

 of the common meniscus, formed when two sucli float- 

 ing bodies are brouglit near to one another, does not 

 tend to lift them ; for the vertical component of the 

 capillary forces, directed toward the centre of con- 

 cavity, is exactly counterbalanced by the weiglit of 

 tlie adhering liquid elevated between them, while tlie 

 horizontal comjponent is free to draw them together. 



So, likewise, the column of liquid sustained in a 

 capillary tube can have no tendency to ' lift the 

 tube ; ' ifor it is evident that the weight of the liquid 

 elevated must exactly balance the xertical component 

 of the capillary forces acting at tlie crowning meniscus 

 within the tube: the horizontal component tends to 

 draw the sides of tlie tube together. 



It is freely admitted tliat my explanation of this 

 class of phenomena may be imperfect, and may be 

 more or less unsatisfactory; but it seems to me that its 

 shortcomings are not to be found in the directions 

 indicated by the objections put on record by the critic. 

 Such elementary facts as have been elicited above 

 could not appropriately find a place in my paper. 



After all, however, the simplest method of reducing 

 tills class of iilienomena to the reaction of elastic 

 films of liquids is the application (as has been done 

 near the close of my paper) of the jirinciple of Gauss; 

 viz., that this reaction "always tends to reduce the 

 surface to the smallest area which can be enclosed by 

 its actual boundary." John LbContb. 



Berkeley, Cal., March 16, 188D. 



A nevir lecture experiment. 



It has long been known, that an iron bar may be 

 permanently magnetized by holding it in the direc- 

 tion of the dipping-needle, and striking it a blow with 

 a hammer. Tlie novelty of this experiment, so far 

 as I am aware, consists in indicating the magnetiza- 

 tion of the bar at the instant the blow is delivered. 

 I use for the purpose a reflecting galvanometer 

 (Kohlrausch"s j)attern), a lantern with detached lens 

 for focusing the reflected beam (or, in the day-time, 

 a porte lumi'ere), a piece of gas-pipe 80 cm. long and 

 45 mm. diameter, and a coil of fine wire large enough 

 to slip freely over the gas-pipe. After carefully de- 

 magnetizing the gas-pipe, the coil of wire is con- 

 nected with the galvanometer, and slipped down 

 against the hand, holding the iiipe about SO cm. from 

 the upper end. With the pipe pointing in the direc- 

 tion of the dipping-needle, a ringing blow is struck 

 on Its upper end, and the spot of light on the screen 

 moves promptly from two to four feet, according to 

 the distance of the screen from the galvanometer. 

 A second blow produces only a very small movement 

 compared with the first one. Reversing the gas-pipe, 

 and again striking it, the change of magnetism is 



indicated by another induced current about equal 

 to the first. The direction of the current is the 

 same as is obtained by moving the coil from the end 

 struck toward the middle of the pipe. By moving 

 the coil along the pipe, before the blow and after it, 

 the induced currents indicate that the temporary 

 magnetism of the pipe produced by terrestrial induc- 

 tion is much weaker than the permanent magnetism 

 produced by the blow. H. S. Carhart. 



HOUGHTON FARM EXPERIMENTS. 



Houghton Farm. Experiments with Indian corn, 



ISSO-Sl, with a summary of the experiments with 



wheat for fort ij years, at Rothamsted. Cambridge, 



Riverside pr., 188-2. 75 p. 1.8°. 

 Agricultural physics. Series i. Nos. 1, 2. 



Meteorology and soil-temperatures. By D. P. 



Penhallow, B.S. Newburgh, Ritchie §• Hull, 



pr. [1883.] 57 p., 5 pi. 1.8°. 



Besides the intrinsic value which, these publi- 

 cations have as reports of carefullj' conducted 

 experiments, thej' possess additional interest to 

 all who have at heart the advancement of scien- 

 tific agriculture in this country, because they 

 are the first public reports of what is here a 

 novel undertaking. The proprietor of Hough- 

 ton Farm, Mr. Lawson Valentine of New York, 

 has, in effect, established upon it an experi- 

 ment-station devoted to the scientific investi- 

 gation of agricultural questions. So far as we 

 are aware, this is the first institution of the 

 kind in the country supported by private 

 munificence, and hence untrammelled hj the 

 demand for results of immediate practical 

 utilit\', and by the mass of miscellaneous 

 chemical work whicli seriously circumscribes 

 the scientific activity of public experiment- 

 stations. The outcome of this form of the 

 ' endowment of research ' will therefore be 

 awaited with much interest. 



The first of these reports gives an account 

 of the field-experiments with Indian corn, exe- 

 cuted by Dr. Manly Miles in 1880 and 1881. 

 These experiments are, in the main, modelled 

 after the famous Rothamsted experiments of 

 Lawes and Gilbert, and are to bo continued 

 through a series of 3'ears, with the design of 

 doing for Indian corn what the English experi- 

 ments have done for wheat and barley. The 

 experimental plots having been laid out and 

 drained in the previous year, a crop of corn 

 was grown in 1880 without manure, in order 

 to test the uniformity of the soil and .establish 

 a basis for subsequent comparisons. This was 

 followed in 1881 by a crop to which various 

 kinds and quantities of manures were applied 

 on tlie several plots, certain plots being left 

 unmannred for comparison. 



