604 



NATURE 



{Oct 3, 1878 



fourteen stations (this is not a fourth part of the number avail- 

 able), and the Indian longitude stations specified above, fifty-six 

 equations treated by least squares give the following elements of 

 the earth's figure : — 



Polar semi-axis <: = 20854895 standard feet. 



Equatorial semi-axis ... a = 20926202 ,, ,, 

 c : a = 292*465 : 293 •465. 

 Bat the evidence of the Indian longitude observations goes to 

 show that the curvature of the surface of India in a direction 

 perpendicular to the meridian is considerably less than that 

 belonging to the spheroid just specified. Possibly this apparent 

 result may be owing to the existence of attractions of the plumb- 

 line seawards at the coast stations. At any rate it suggests the 

 re-investigation of the ellipsoidal form of the earth : and the 

 result of a formidable calculation is that the ellipsoid best repre- 

 senting all the observations has the following semi-axes : — 



a = 20926629 h = 20925105 c = 20854477, 



and the ellipticities of the two principal meridians 



_i_ and — L-. 

 289-5 2958 



The longitude of the greater axis of the equator is 8° 15' W. of 

 Greenwich — a meridian passing through Ireland and Portugal, 

 and cutting off a portion of the north-west corner of Africa ; in 

 the opposite hemisphere this meridian cuts off the north-eastern 

 corner of Asia and passes through the southern island of New 

 Zealand. The meridian containing the smaller diameter of the 

 equator passes through Ceylon on the one side of the earth and 

 bisects North America on the other. Thus the division of the 

 earth by the meridian plane of the greater axis of the equator 

 corresponds very nearly with the ordinary two-circle representa- 

 tion of the earth, the one showing the Eastern hemisphere the 

 other the Western. 



Such is the result of the 'calculation, and it is a somewhat 

 remarkable result when considered in connection with the actual 

 physical features of the globe, and the distribution of land and sea 

 on its surface. But too mu.ch confidence must not be placed in 

 it ; many more measurements would be necessary to establish 

 this figure as a reality ; as yet it is merely indicated by the exist- 

 ing observations, and the amount of the eccentricity of the equator 

 shown above is really very minute. 



It is to be observed — returning to the spheroidal figure and 

 comparing this new result with that quoted above from the 

 volume of " Comparisons of Standards" — that the effect of the 

 new work in India has been to increase the radius of the equator 

 by 140 feet, and to diminish the polar radius by 226 feet. 



There are several short arcs on the European continent which 

 might have been used in addition to the long arcs, but the influ- 

 ence of these on the resu't would have been almost imperceptible. 

 The details of the American Coast Survey oblique arc are not 

 yet published. 



Notwithstanding the immense additions to geodetical measure- 

 ments and to the data of the problem of the figure of the earth 

 since Bessel's investigations {1841), it is with a good deal of 

 truth that Karl Maria Friederici says that Bessel's results are still 

 universally adopted by scientific men. And this must be con- 

 sidered a very remarkable instance of the influence of a ttame. 

 Bessel was a splendid mathematician ; his works are characterised 

 by great elegance ; and in this case his fame is a set-off against 

 the increase of data subsequent to his time. But Bessel could 

 only use one-fourth part of the present English arc (and the ter- 

 restrial measure of this arc as used by him was some 200 feet in 

 error), and one-third of the present Russian arc. In his time the 

 English, Russian, and Indian arcs amounted in all to less than 

 27° ; now they exceed 57°. Hence Bessel's figure of the earth 

 cannot be considered anything else than obsolete, however excel- 

 lent it may have been six-and-thirty years ago. 



The operations which are being conducted with so much 

 activity on the European continent and in India must shortly 

 put us in possession of great additions to the data of the problem, 

 especially through the agency of the electric telegraph. As a 

 specimen of the precision now attainable in the determination 

 of longitudes by galvanic signals, we may quote the three results 

 obtained at different times and in different ways for the difference 

 of longitude of Greenwich Observatory and Harvard Observatory 

 (Cambridge, Massachusetts). They are as follows : — 



h. m. s. 



In 1866, by Anglo-American cables 4 44 3 1 '00 



In 1870, by French cables to Duxbury 4 44 30*99 



In 1872, by French cable to St. Pierre 4 44 30 "96 



Doubtless there is a certain amount of good fortune in this, 

 but nevertheless the accordance is highly satisfactory. 



AN EXPERIMENTAL INVESTIGATION OF 

 THE STRUCTURE OF FLUID COLUMNS 

 WHICH ARE AFFECTED BY SOUND 



VU'HEN a fluid escapes from a contracted opening, it may 

 form a column, which throughout the greater part of its 

 length has the same sectional shape as the opening. This kind 

 of column may be called prismatic. 



It may after leaving the opening form an expan- 

 sion, this expansion being succeeded by another 

 at an angle (usually a right angle) to it ; and this 

 latter by another, and so on. This kind of column 

 may be called segmental (Fig. i). 



An example of the first is obtained when the 

 column proceeds from a true cylinder, truncated 

 at right angles to its axis, and is very difficult to 

 obtain. 



A segmental column is easily obtained from 

 the end of a partially closed glass tube. 



Segmental columns are sensitive, prismatic 

 columns not sensitive, to sound. 



The character of a jet is determined by con- 

 necting with a water supply. 



The apparatus. Fig. 2, is intended to show the 

 structure of a segmental column, a, b, c, d is & 

 piece of cork 2\ in. X I in. and i inch thick. 

 Pieces of glass tube 2 inches long serve as axes for 

 the corks C c. Each cork is pierced at right 

 angles to its axis to support a jet j. An India* 

 rubber T-piece connects the jets with gas or water 

 supply. 



It wiU be seen that the arrangement permits of 

 the jets being inclined to each other at any angle 

 by the movement of the corks round their axes ; 

 and a lateral adjustment may be obtained by 

 sliding them along their axes. 



To make the jets : the middle of a long piece 

 of glass tube is contracted in the blowpipe flame ; 

 when cold a sharp scratch is made in the middle 

 of the contraction, and the tube broken through. 

 Two perfectly equal jets are thus obtained. 



Experiment I. — Arrange the jets at an acute 

 angle and connect with a water supply. The 

 segmental column will be obtained. The first 

 (primary) expansion being at right angles to the plane of the 

 jets. 



Experiment II. — Keeping the water supply as before, increase 

 the angle of the jets ; the segments will become more marked and 

 the length of the entire column 4ecreased. At a certain angle 

 the primary expansion becomes so great that the cohesion of the 



different parts will be overcome, and the column be fan-shaped. 



The ordinary fish-tail burner furnishes a familiar example of 

 this extreme segmentation. t, • j • 1. 



^oie. — As every degree of segmentation may be obtained with 

 suitable inclination of the jets, it follows that a segmental column 

 really consists of two similar ones, meeting at an angle. 



