434 



NATURE 



[OCTODER 6, 1910 



a colour effect in the observations, to which a refer- 

 ence is made in Nature (vol. Ixxv., p. 234), further 

 examination has failed to disclose any systematic error 

 attributable to that cause, while the arrangement and 

 discussion of the several series of measures — Dr. 

 Elkin himself made no fewer than seven — exclude 

 the possibility of any personal peculiarity or habit 

 escaping detection. The adopted parallax values for 

 each of the three observers are as follows : — • 



Probable 

 Observer. Parallax. Error. 



Elkin ... +0-051 

 Chase ... +00S5 

 Smith ... +0-050 



After an elaborate system of "weighting," for de- 

 tails of which we must refer to tlie original paper, 

 the finally adopted value of the parallax of .Arcturus 

 is o'o66" ±o'oo6". 



The interesting stars 61 Cygni and Groombridge 

 1830, notwithstanding the repeated attempts that have 

 been made to determine the parallax, are among those 

 stars of which it has been thought desirable to repeat 

 the measures. Without entering into further parti- 

 culars, it may be said that the results are equally 

 consistent as those obtained in the case of Arcturus, 

 and command equal confidence. 



The grand result of the work at Yale, which has 

 occupied the three observers for some years, is to 

 assign a parallax to 200 stars, with an accuracy that 

 we believe has not been attained elsewhere. The 

 three stars in the Pleiades not being included, we have 

 here a catalog-ue of 197 stars, which Dr. Elkin forms 

 into groups depending on magnitude and proper 

 motion. This table is so small that it can be con- 

 venientlv given here. It may seem but a modest out- 

 come for so many years of careful and anxious work, 

 but those who appreciate it most will be warmest in 

 their congratulations to Dr. Elkin and his able col- 

 leagues on the satisfactory completion of a task of 

 no common difficulty. The table into which so much 

 work is compressed is as follows : — 



The number in brackets after the parallax signifies 

 the number of stars in each group. As Dr. Elkin 

 remarks, "There is, with slight exception, nianifest a 

 very decided seauence of values, both with respect 

 to magnitude and size of proper motion, such as one 

 might expect." W. E. P. 



THE PERFILOGRAPH. 

 ' I 'HE perfilograph is an ingenious instrument for 



■*■ recording sjraphically the undulations of the 

 bottom of a channel in depths up to about six or 

 seven fathoms. It is the invention of .\ugustus 

 Mercau, an Argentine engineer, by whom a paper was 

 read at Buenos Aires before the Naval Section at the 

 recent meeting of the International American Scien- 

 tific Congress, in the course of which the instrument 

 was fully described. The principles on which its 

 construction depends and the practical results obtained 

 from its use appear to present some points of interest. 



A heavy weight of from 150 to 200 lb. being slowly 

 dragged along the bottom by a wire rope attached to 

 the stern of a steam launch, it is obvious that as the 

 depth changes the inclination of the wire will vary. 

 By an ingenious mechanism, the sine of the angle 



NO. 2136, VOL. 84] 



made by the wire with the horizontal plane is regis- 

 tered graphically in parallel ordinates on a roll of 

 paper, which is slowly unwound by means of clock- 

 work at a rate proportionate to that of the vessel. 

 The lengths of the ordinates, being proportional to 

 the sines of the varying angles, represent the undula- 

 tions of the bottom referred to the horizontal plane, 

 and are registered on a convenient scale on the paper 

 by means of a system of levers. 



The instrument, mounted in the stern of the launch, 

 is placed accurately at a height of 5 feet above the 

 water-line, and the depths are measured from a zero 

 line drawn by a pencil pressing against the roll of 

 paper as it is unwound. The system of levers by 

 which the sines of the angles are registered is con- 

 nected to a length of tubing of small diameter, 

 through which a thin guiding wire passes. One end 

 of this wire, which is about 50 feet in length, is 

 secured to a spiral spring attached to the weight on 

 the bottom ; the other end is led underneath the base 

 of the instrument and secured. The spiral spring 

 yielding to a strain of about 150 lb., the tension on 

 the guiding wire is automatically relieved by throw- 

 ing the excess of strain on to the towintr cable, the 

 length of which is adjusted accordingly. The guiding 

 wire, being thus kept taut by a strain not exceeding 

 150 lb., the length of tubing through which the wire 

 passes takes up an inclination to the horizontal de- 

 pendent on the depth of water, and in so doing it 

 actuates the system of levers with which it is con- 

 nected. 



The speed at which the weight can be towed should 

 not exceed three or four knots. There is an arrange- 

 ment for marking on the paper the instant at which 

 the position of the vessel mav be fixed by means of 

 se.xtant angles. The horizontal scale of the diagram 

 may thus be determined between successive " fixes " 

 by actual observation, independently of the rate at 

 which the paper is being unrolled or the speed at 

 which the vessel may be moving. Unless these two 

 factors remain constant throughout the run, the hori- 

 zontal scale will be subject to variation. It is desir- 

 able therefore to reconstruct the diagram, so far as 

 its horizontal components are concerned, from the 

 data afforded bv the "fixes." 



The horizontal scale of the diagram is rotighly about 

 i/iooo or about 70 inches to the nautical mile; the 

 vertical scale is about \ inch to a foot. The instru- 

 ment has been adopted by the .\rgentine Hydrographic 

 Service, and has been in constant use for some time 

 past. It is understood that the results are considered 

 quite satisfactory. 



.'\n opportunity of witnessing a practical trial was 

 courteously afforded to the present writer by the 

 .•\rgentine naval authorities. The instrument was 

 readilv set up and adjusted, and several sectional lines 

 were run across the dredged channel leading to the 

 docks at Buenos .\ires. The resulting diagrams over 

 the same section run in opposite directions agreed 

 accurately, and no difficulty whatever was experienced 

 during the trials. 



The following advantages have been claimed for the 

 instrument: — (i) Continuity of the section traced; (2) 

 accuracy of results; (3) rapidity as compared with 

 ordinary methods ; (4) economy of skilled labour ; (5) 

 f.acilitv of manipulation ; (6) capabilitv of use in 

 circumstances of sea and weather when accurate 

 soundings by the lead could not be obtained. 



The trials were carried out in open water with its 

 surface considerablv disturbed by a fresh breeze, and 

 afTorded a verv fair test of the capabilities of the 

 instrument. There is certainly a source of error 

 owing to the motion of the vessel. The section as 

 shown on the diagram is necessarily a combination of 



