7o8 



NATURE 



[Oct. 31, 1878 



Tablk I. 



It will be seen from this table that the value of -f " " is as 



sm ^ 



nearly a constant as can be expected from this kind of measure- 

 ment. 



Table II. gives the results obtained with the same coil and 

 needle as before, but with the current unaltered in strength (one 

 Bunsen's cell suitably reduced by the insertion of a small resist- 

 ance). The order of experiments is shown by the arrows. 



Table II. 



The smaller value of the constant at the top of each column is 

 doubtless due to slight mechanical inaccuracies in this experi- 

 mental instrument. 



Table III. gives the results obtained with the copper band 

 provided with stout leading wires and with the needle fixed to 

 an axle. The resistance of the copper band, including the leads, 

 was only -001 Siemens' units. Three Bunsen's cells connected 

 parallel Were used without additional resistance. 



Table III. 



In this table the greatest difference from the mean of the 

 constant (2-33) is not more than -8 per cent. 



The foregoing experiments having shown that the measure- 

 ments with this instrument are, as to exactness, in no way inferior 

 to those with the usual form of tangent galvanometer, I also 

 employed it for the currents ef dynamo-electric machines. 



The first of the«e experiments was made with a Siemens' 

 machine of smallest size. Besides the galvanometer an electric 



lamp was in circuit. The strength of the current and the in- 

 tensity of the light was measured, and at the same time the 

 number of revolutions of the armature counted. The results- 

 are given in the next table. 



Table IV. 



Revolutions 

 of armature. 



860 

 851 



Deflection a 

 (sin ip = '2) 



38 



37 



•7813 

 -7536 



3-906 

 3-768 



Intensity of 

 light in 

 standard 

 candles. 



3200 

 2750 



The second experiment was made in the same way as the pre- 

 ceding, but with a Siemens' machine of medium size. The 

 results are given in 



Table V. 



Revolutisns 

 of armature. 



660 

 696 

 692 



Deflection a 

 (sin ='i) 



28 



33-5 



33 



•5317 

 -6619 

 -6494 



tan a 

 sin <p 



5-317 

 6-619 

 6-494 



Intensity of 

 light in 

 standard 

 candles. 



4100 

 6400 

 7700' 



The deflections in the experiments with the small machine 

 were taken with the galvanometer ring at an inclination, the 

 sine of which is equal to -2 ; with the larger machine the sine of 

 the angle of inclination was equal to -J. The column headed 



^^IL? gives in both cases the tangent of the deflection which 



sin </) 



would be obtained with the vertical ring. 



By these two tables 1 intend merely to show that even such 

 powerful currents which give a light of thousands of candles 

 produce readable deflections with a suitable inclination of the 

 ring. 



I may add that the method I have just described to reduce the 

 action of a coil upon the magnetic needle by turning it round a 

 horizontal axis will scarcely be limited to the tangent galvano- 

 meter, but that this method very likely can be used with other 

 galvanometric apparatus for many purposes where shunts are 

 not desirable. EuGEN Obach 



GULF-WEED^ 

 "PROM the time of Columbus to the present day the gulf -weed 

 ■^ growing in the "Sargasso Sea " has attracted the attention 

 and excited t-he interest of all voyagers who have crossed the 



' With other carbon points than used before. 



= Om de under Korvetten Josephines _,e.-x.-^^^AiOT\, sistliden sommar (1869), 

 insamlade Algerne. Af J. G. Agardh, Ofversigt af Kon^l. Vetenskaps-Aka- 

 demiens Forfiand linear, 1870, No. 4, Stockholm. ti nc c 



Enumeration of Algae collected by Mr. Moseley, Naturalist to H.M.S. 

 Challenger, at St. Thomas, Bermudas, Coast of Brazil, Cape de Verde 

 Islands, St. Paul's Rocks, Fernando de Noronha, Tiistan d'Acunha, Inac- 

 cessible Island, Simon's Bay, Seal Island, Marion Island. Heard Island, 

 and Keiguelen's Island. By Prof. G. Dickie, M.D., F.L.S., I-innean 

 Ssciety's Journal — Botany, vol. xiv. 



