3o8 



NATURE 



{Jan. 24, 1889 



A pyramid is being raised on the summit of the mountain, which 

 it is hoped will dissipate the superstition among the natives 

 below that no one can ever reach the top. 



Captain Trivier, a French naval officer, has left France to 

 undertake an expedition across Africa. One of his chief objects 

 will be the exploration of the Lualaba and its tributaries, and 

 more especially the Lukuga, the outlet of Lake Tanganyika, 

 about the real nature of which there has been so much con- 

 troversy. Captain Trivier will follow the Lukuga to the lake, 

 and make a careful report on its actual condition. Captain 

 Hore, who has been more than ten years on the lake, has just 

 returned home. He states that during the whole period of his stay 

 on the lake it has steadily decreased in size ; its level has fallen 

 quite 15 feet, but the Lukuga still flows out with a rapid current. 

 This it will continue to do until its muddy bed is worn down to the 

 rock, when it will cease to be an outlet of Tanganyika. Captain 

 Hore seems to think the lake will go on decreasing in size. 

 Captain Trivier will cross to Ujiji and endeavour to make his 

 way to the east coast at Bagamoyo. 



The first number is to hand of the National Geographic 

 Magazine, the organ of the recently founded " National 

 Geographic Society " of the United States. The work of the 

 Society, of which all the leading officers of the U. S. Survey are 

 members, promises to be of much higher scientific value than 

 that of the American Geographical Society of New York. 

 The Society has 200 members. Among the articles in this 

 number are "Geographic Methods in Geologic Investiga- 

 tions," by Mr. W. M. Davis ; "Classification of Geographic 

 Terms by Genesis," by Mr. W. J. McGee ; "The Survey of 

 the Coast," by Mr. H. G. Ogden ; and the " Survey and Map 

 of Massachusetts," by Mr. Henry Gannett. 



Captain Wahab reports as follows regarding the survey work 

 accomplished by himself and one sub-surveyor while with the 

 Hazara field force : — " Up to the end of the Ahazai country we 

 have a complete survey extending a good way west of the Indus, 

 and a certain amount of reconnaissance work in the Chagarzai 

 country up to about Judbai. North- east of the Black Mountains 

 we have surveyed from Nandihar (the limit of this survey in the 

 1868 expedition), north to the range beyond AUahi, and west to 

 the hills overlooking the Indus. We have fixed the course of 

 the river up to say 15 miles north of Thakot, and I have 

 sketched, on the ^-inch scale, as much as possible of the country 

 between the Indus and the Swat Valleys, what I could see from 

 the Chel Mountain and the Ghorapher Pass. I have made three 

 stations, and fixed a number of points in the lower ranges 

 between the snowy peaks fixed by the Great Trigonometrical 

 Survey and our frontier, which I hope may be useful on future 

 occasions. While I was triangulating on the top of Chel, Imam 

 Sharif went down the hill to Pokal, for the day, and got in most 

 of the Allahi Valley. There is a gap in the survey of the Indus 

 Valley from the bend west of Thakot down to Judbai, which 

 cannot be seen without going into the Chagarzai country, but 

 even if vve do not go, I have got the course of the river practically 

 fixed within about half a mile one way or the other." 



ELECTRICAL NOTES. 

 F. KoHLRAUSCH has just made a fresh determination of the 

 ohm. He makes it equal to 106 '32 centimetres of mercury 

 I square millimetre in section. 



Prof. Rowland has made preparations to repeat his classical 

 Berlin experiment by which he demonstrated the fact that a 

 static electrical charge in motion acted like a current. He is 

 going to use higher speeds and higher electrification, and it is 

 therefore hoped that he will get accurate quantitative deter- 

 minations. 



At Paisley, an electric discharge, which seriously damaged a 

 chimney and its defective lightning-conductor, also killed a 

 quantity of fish that were in a pond close by in which the con- 

 ductor was earthed. When will people take the precaution to 

 examine their lightning protectors ? 



Dubs {Centralblatt fiir Electrotechnic, 1888, No. 28) has 

 shown that a strong blowpipe or oxy hydrogen flame from one 

 carbon to another sets up an E. M.F. which would fully account 

 for the opposing E. M. F. of the arc. 



A NEW mode of regulating dynamos for constant current and 

 constant potential has been devised by the Waterhouse Com- 



pany in the United States by means of a tliird brush slightly in 

 advance of the positive brush, and an external variable shunt 

 circuit which can be adjusted automatically or by hand. The 

 desire to evade patents has at least one merit — it exercises the 

 faculty of invention and stimulates design. The Electrical 

 Engineer of New York (December 1888) has an excellent 

 paper by Mr. Caldwell on this third brush. 



It is sometimes asserted that the unit of work— the erg—\% too 

 small to be of any use, but Prof. Langley has shown that the per- 

 ception of the colour crimson is produced by an expenditure 

 of energy upon the retina, which can be represented by 10"^'* 

 horsepower, or O"ooi of an erg ; while the sensation of green 

 is due to o'coocoooi of an erg. 



Helmholtz has shown that if an invisible jet of steam be 

 electrified or heated it becomes visible with bright tints of 

 different colours according to the potential or the temperature. 



Dr. Gore, F. R. S., has submitted to the Royal Society a new 

 instrument of research, which he thus describes : — " Take two 

 small glass cups containing known volumes of distilled water. 

 Form two voltaic cells of them by means of strips of stout wires 

 of unamalgamated zinc cut from the same piece, and two small 

 sheets of platinum, also cut from the same piece. Connect them 

 together in series to a sufficiently sensitive galvanometer, so that 

 the currents from the two calls oppose each other, and produce 

 no visible deflection of the needles. This arrangement consti- 

 tutes a 'voltaic balance,' and is extremely sensitive to change 

 of chemical composition of the liquid in one of the vessels. 

 Make an aqueous solution of known strength of the substance, 

 and add it in sufficiently small quantities at a time to the water 

 in one of the cups until the needle of the galvanometer visibly 

 commences to move, and note the proportion of the substance 

 and of water then contained in that vessel. As the amount of 

 energy required to move the needle is the same in all cases, the 

 different numbers thus obtained with different substances repre- 

 sent the relative amounts of voltaic energy of those substances. 

 And as each substance and mixture of substances gives a different 

 number, it is possible by this method to detect substances, to 

 ascertain the degrees of strength or concentration of liquids, to 

 ascertain whether a substance contains a soluble impurity, &c. 

 The method also is in many cases an extremely sensitive one." • 



Prof. J. J. Thomson (R.S., January 17, 1889) has examined 

 the screening influence of conducting plates upon alternating 

 currents of great frequency, and has deduced thereby the resist- 

 ance of electrolytes and of graphite. He shows that the screen- 

 ing effect depends on the conductivity and thickness of the plate 

 and upon the frequency of the alternations. The secondary in- 

 duced currents are confined to the skin of the plate next to the 

 primary, the thickness of this skin varying inversely with the 

 cinductivity of the plate and the frequency of the currents. Thus 

 a thin plate of badly conducting material will be efficient with 

 currents of great frequency, such as those of the rate 10^ per 

 second ; while a thick plate of the best conducting material will 

 not be sufficient to screen off currents of low frequency, such as 

 those with a rate below 10" per second. Thus to measure the 

 resistance of electrolytes it is necessary to have vibrating elec- 

 trical systems such as those examined by Hertz, whose frequency 

 is of the former class ; and if two different plates produce the 

 same screening effect, their thickness must be proportional to 

 their specific resistances. He supports Maxwell's theory that 

 the rate of pr.^pagation of electrostatic potential is practically 

 infinite, a point called in question by Hertz ; and he agrees with 

 Mertz that the rale of propagation of electro-dynamic action is 

 finite and measurable. He shows that the rate of propagation 

 cf an electro-magnetic disturbance through a metallic conductor 

 and through the surrounding dielectric is the same, and this 

 differs from one of Hertz's conclusions. But he also shows that 

 this is not so when the conductor is a dilute electrolyte' or a rare- 

 fied ga^. In such a case there would be interferences and stand- 

 ing vibrations. Hence the striae in so-called vacuum-tubes. He 

 also concludes that the relative resistance of electrolytes is the 

 same when the current is reversed a hundred million times a 

 second as for steady currents. 



Someone in the United States has proposed to call static 

 electricity "amberism." It is a good analogue to "galvanism " 

 and to "magnetism." It would be well to introduce some term 

 to relieve the word "electricity" from the dreadful abuse 10 

 which it is now subjected. The Board of Trade in their draft 

 Provisional Orders are using it in three distinct and different 



