August 27, 1908] 



NATURE 



593 



quite independently of any quadrant, so mag. east 

 would read N. 90° E., and mag. west N. 270° E. 



The circles of small instruments are graduated to 

 degrees, and so the azimuths are read to degrees and 

 estimated to half degrees. In instruments with larger 

 circles, whether it be a circular protractor for reading 

 azimuths on maps, or a theodolite for determining 

 them, the degree can be read to -j^jth of a degree, or 

 even more finely, by means of a device called a 

 vernier, on whicli it is useful to dwell a little, as many 

 regard it as of a recondite and mysterious nature and 

 avoid it accordingly, whereas it is as simple as it is 

 useful. 



The vernier is a short scale, constructed so that its 

 divisions are smaller by a definite and convenient 

 amount than those of the scale with which it is used. 

 In a very simple case this difference amounts to y'oth 

 of a scale division, and the vernier is made so that its 

 ten divisions are equal in length to nine of the 

 primary scale. One extremity of the vernier scale is 

 th? reference point, or zero, and if this be coincident 

 with a scale division, the remaining divisions of the 

 veinier will be separated from divisions of the scale as 

 indicated below : — 



Division o of vernier coincident with division of scale. 



If then the vernier be in such a position in relation 

 lo the scale that its fourth division is coincident with 



Fig. I. — Model of a vernier showing how the divisions on a straight lir.e can 

 be divided into tenths. Here the vernier (btlow) has its zero point 

 coincident with a division on the scale. 



a scale division, the zero mark must be j*(fths removed 

 fiom a scale division, and so on. In this way the 

 coincidence of the vernier and scale divisions indicates 

 the fractional part to be read. 



It is quite easy to make a wooden model of a fixed 

 scale and a sliding vernier; a little manipulation of 

 this will make everything quite clear. 



^__.^^^^^^^^^^ 



I I I I I M I I 



I I I I I I I I I 



III I I I 11 



I II I 



-\Sg»fSSB^^B 



Fin. 2. — Here the zero of the vernier is between the 6th and 7th divisions of 

 the scale. The third division of the vernier is coincident with a division 

 of the line, so the reading is 6y^fi. 



In a circle graduated to half degrees, the vernier 

 is so constructed that its thirty divisions are equal in 

 length to 29 divisions of the circle. The vernier 

 divisions are therefore smaller than those of the 

 circle by 



Ax 30'='' 

 NO. 2026, VOL. 78] 



and the vernier is said to read to one minute. Thus 

 to set the index of the vernier at the reading 30° 18', 

 first adjust it to the position 30°; then move the index 

 towards the mark corresponding to 31°, and stop 

 when the eighteenth division of the vernier becomes, 

 coincident with a division of the scale. 



Fig. 3. — .^ vernier applied to a circle enabling azimuths(or any other angle) 

 to be read to tenths of a degree. ^ 



•So much, then, for the reckoning and readings 

 of azimuth, measurements on a horizontal plane. 



AWiludcs. 



For the reckoning of altitudes, which of course are 

 observed with a vertical circle, the degree system is 

 alone used, the fineness of the reading depending 

 upon the size and graduation of the circle employed. 

 The vertical circle is generally graduated into four 

 quadrants of 90°, the zeros lying in the horizontal 

 line. We can thus read elevations or depressions in 

 degrees, or some smaller division of a degree. 



NORM.AN LOCKYER. 



THE PERCY SLADEN TRUST EXPEDITION 

 TO MELANESIA. 



T X the autumn of last year the trustees of tlie Percy 

 ■*■ Sladen Memorial Fund made a grant to Dr. 

 W. H. R. Rivers, F.R.S., of St. John's College, Cam- 

 bridge, to enable him to make detailed sociological 

 studies in the Pacific, and more particularly to study 

 mother-right communities in the Solomon Islands, and 

 to trace the details of the transition from mother-right 

 tJ father-right. Dr. Rivers left England at the end 

 of No\'ember, and, after staying a short time in the 

 United States, proceeded to the Hawaiian Islands. 

 Dr. Lewis H. Morgan, in his classical work, 

 " .Ancient Society," says (p. 403), " Among the 

 Hawaiians and other Polynesian tribes there still 

 exists in daily use a system of consanguinity which 

 may be pronounced the oldest known among man- 

 kind. ... It is the simplest, and therefore the oldest 

 form, of the classificatory system." 



The investigations of Dr. Rivers into the kinship 

 systems of the two groups of Torres Straits islanders 

 (Reports Camb. Exped. to Torres Straits, vols, v., 

 vi.), and subsequent comparative studies led him to 

 the conclusion that " as the Polynesian languages 

 have arisen by simplification of tho.se of the 

 Meianesian family, so have the Pol^'nesian kinship 

 systems arisen by simplification of a variety re- 

 sembling those found among Papu.in and Meianesian 

 peoples at the present time " (Rivers, " Anthro- 

 pological Essays presented to E. B. Tylor," 1907, 

 p. 314). In an essay (based on information obtained 

 from natives by means of the genealogical method) 



