September 11, 1885.] 



SCIENCE, 



205 



velocity increases, nearly inversely as the square of 

 tlie velocity; 3°, that increases as the logarithm of 

 the radius of the cylinder, the radius heing measured 

 hy a unit differing from the earth's radius by a 

 small quantity, which is a function of the velocity. 

 Second, in the case of a widely extended group of 

 small bodies evenly distributed in space, and having 

 speeds all equal, but directed towards points evenly 

 distributed over the celestial sphere with the earth 

 moving in a right line through them, it is shown 

 that, for those which do not strike the earth, but 

 only affect it by their attraction, the effect will be 

 an exceedingly minute acceleration of the earth's 

 motion, if the latter is less than that of the bodies, 

 €ven though the group is infinite in extent. If the 

 earth's velocity is greater than that of the bodies, 

 their total effect will consist of two parts; a very 

 minute retardation of the earth's motion depending 

 in amount upon the absolute velocity of the bodies, 

 and another retardation depending upon the assumed 

 extent of the group. In conclusion, the effect of 

 bodies striking the earth or moon is manifold greater 

 than that of those only passing near ; and since it has 

 before been shown that any admissible magnitude of 

 meteoroids would make the effect upon tlie moon's 

 mean motion of those which strike it only a minute 

 fraction of the observed acceleration, still less can 

 any action of those passing near the moon have any 

 appreciable effect. The hour of adjournment pre- 

 vented any discussion of this interesting paper. 



The first paper of Friday's session was by Prof. Wm. 

 Harkness of the U. S. naval observatory upon the 

 fiexure of transit instruments. The time- observa- 

 tions of the different transit-of-Yenus parties in 

 1874 and 1882, — and the latitude observations as well, 

 — were made with transit instruments of the ' bent ' 

 or 'broken' pattern; i.e., a totally reflecting prism is 

 placed in the tube of the axis, and thus one-half of 

 the axis itself forms a part of the telescope tube, 

 the eye-piece and micrometer being at one end of the 

 axis. This form, while allowing great convenience 

 and rapidity of manipulation, introduces newdifiicul- 

 ties through the flexure in the support of the central 

 prism; and the discussion of these has led Professor 

 Harkness to make a thorough investigation of the 

 flexure of transit instruments from the most general 

 standpoint. The details are of too technical a char- 

 acter for popular presentation ; and we can only state 

 the general nature of the subject, and give a brief 

 summary of the points brought out. Astronomers, 

 in the most exact measurements possible with their 

 instruments, have always been obliged to consider 

 even the most rigid of them as elastic, and as bend- 

 ing differently under the force of gravity as they are 

 swung into different positions. But if they are en- 

 tirely symmetrical in construction with reference to 

 a vertical plane, it is generally assumed that the 

 entire flexure takes place parallel to that plane; and 

 hence that the line of collimation determined by re- 

 versal upon a collimator, or by a pair of opposite col- 

 limators, is at right angles to the axis when corrected 

 for inequality and irregularity of pivots. But the 

 special point of Professor Harkness' s paper was, that, 



on account of unequal elasticity in the different parts 

 of any instrument, this condition could only be cer- 

 tainly fulfilled when the direction of gravity through 

 the instrument was not changed by the operation. 

 This could only be done by reversal either upon a 

 zenith-collimator or over the nadir, and in these two 

 positions only could the line of collimation be consid- 

 ered as rigorously at right angles to the axis. The 

 other conclusions were, that for the particular 

 zenith distance at which a line of collimation is de- 

 termined, that line possesses the essential properties 

 of a line at right-angles to the axis, but for no other 

 zenith distance ; and that flexure at right angles to 

 the meridian consists of two parts, the larger of 

 which is measurable by a pair of collimators, but the 

 smaller is only determinable by star-transits. For 

 field instruments this metliod would be feasible; but 

 in the case of larger meridian instruments, which are 

 supposed to correct the positions of the stars, this 

 would hardly be allowable in fundamental work. 

 Prof. H. M. Paul of the naval observatory remarked 

 that the results of the paper emphasized anew the 

 necessity, in the great bulk of meridian observa- 

 tions, of work in zones, the positions of the zero- 

 stars in these zones depending upon some good 

 fundamental system like that of Auwers; and also, in 

 the formation of such a system of fundamental posi- 

 tions, the advantage of giving greater weight to the 

 work of different observatories upon the stars which 

 culminated near their zeniths, provided they could 

 determine their collimation by reversal upon a zenith 

 collimator. 



The next paper was by Prof. Gr. W. Hough, director 

 of the Dearborn observatory at Chicago, describing 

 some improvements recently introduced in the print- 

 ing-chronograph, first designed and brought into use 

 by himself at the Dudley observatory in 1871. This 

 instrument is designed to print upon a fillet of paper 

 the minutes, seconds, and hundredths of seconds. 

 indicated by the clock which controls it, at any in- 

 stant when an observing-key is closed by the observ- 

 er's finger. The impression is made from the surface 

 of three continuously running type-wheels, the swift- 

 est of which revolves once per second, and is con- 

 trolled each second by the standard clock. The 

 recent improvements consist in engraved type on the 

 face of the wheels in place of the rubber ones used 

 at first, which required too frequent renewal; and of 

 the substitution of a direct blow by an electro-mag- 

 net upon the type-wheel fillet, thus making the ap- 

 paratus much more light and compact than the old 

 form. For this Professor Hougli uses three cells of 

 a storage battery, each of about two volts electro- 

 motive force, and from 0.3 to 0.4 of an obm resist- 

 ance, thus furnisliing a strong current for the printing- 

 magnet. The cells are kept permanently coupled to 

 the chronograph, and are charged by eight small 

 gravity cells having a resistance of 7 to 10 ohms 

 each. He claimed that it was perfectly reliable, and 

 eminently a labor-saving machine; and described its 

 use in making transit observations as a luxury that 

 no one would do without after trying it, the mean 

 of the seconds and hundredths being taken directly 



