338 



NATURE 



\7uly 25. 1878 



found to be of great service in exploring expeditions, and 

 they are still being used by parties engaged in opening 

 up new pastoral country. Several of the animals have 

 recently been lent to squatters for expeditions to the 

 country on the Western Australian border, the MacDon- 

 nell ranges in Central Australia, and elsewhere. 



From the new issue of Behm and Wagner's "Be- 

 volkerung der Erde," we learn that the present population 

 of the earth is estimated at 1,439 millions as compared 

 with 1,424 millions given in the previous issue. This 

 increase results mainly from the recent censuses which 

 have been taken in several countries. This population is 

 <livided among the several continents as follows : — 

 Europe, 3 1 2,398,480 ; Asia, 83 1 ,000,000 ; Africa, 205,2 1 9,500 ; 

 Australia and Polynesia, 4,411,300; America, 86,116,000. 

 This new issue contains the first map we have seen of 

 New Zealand with the recent division into counties, in 

 substitution for the old division into provinces. A census 

 according to counties cannot, however, be taken till 1881. 

 The North Island has thirty-three and the South Island 

 thirty-one counties. 



Mr. Stanford has issued a very useful shilling Treaty 

 Map of South-Eastern Europe and Armenia, showing 

 the boundaries of the New Bulgaria and Eastern Rou- 

 melia, the accessions to Austria, Russia, Montenegro, 

 Servia, and Roumania, and all the other changes which 

 have been made by the recent Congress. The new 

 features are shown with unmistakable clearness. Mr. 

 Stanford is also preparing a large scale map of Cyprus, 

 showing not only the physical, but also the geological, 

 agricultural, and other features of our latest acquisi- 

 tion. 



An expedition to the mouth of the Yenisei River left 

 St. Petersburg last week. Principally at the instigation 

 of a Moscow commercial firm eight steamers laden with 

 corn, spirits, nitre, and other goods will soon start on the 

 new sea-road to Siberia, their return cargoes consisting 

 of wood and tea. 



Mr. Gordon Bennett proposes to send the yacht 

 Dauntless on a voyage of discovery to the Polar Seas, 

 vid Spitzbergen, in addition to the Pandora, which will 

 attempt to reach the Pole by another route. 



METHOD OF 

 VIBRATIONS 

 GRAPHY* 



RECORDING ARTICULATE 

 BY MEANS OF PHOTO- 



a right angle. This wire serves to connect the vibrating disc 



T^HE object of this paper is to describe a method of obtaining 

 ■*• photographs of minute vibrations on a magnified scale. 



A plane mirror of steel, A, is supported by its axis in the 

 metal frame B. The ends of the axis are conical, and carefully 

 fitted into sockets in the ends of the screws c, c. On the back 

 of the mirror is a slight projection, D, pierced by a small hole. 



The vibrating disc, as hitherto employed, is a circular plate of 

 ferrotype iron, 2| inches in diameter, screwed to the back of a 

 telephone mouthpiece of the form invented by Prof. John 

 Peirce, and now universally used. From the centre of the back 

 ofahiSjdisc a stiff steel wire projects, tlie end of which is bent at 



Back view of. mirror, actual sixe. 

 with the mirror by hooking into the hole in D, as represented in 



M^vi^'^'vis4yU4-M^^^\^4^'4^^^44^^--4-Ms 



E {LONG. ENGLISH) 



mwm-^i^ 



I (ENGLISH) 



o 



Uiniunjiirii 



^mmi}^m 



uauuuuuuuui 



the figure. The mirror frame and the vibrating disc are kept in 

 a fixed relation to each other by a block of hard wood, to which 

 both are firmly screwed. The mirror is set with its axis parallel, 

 and its reflecting surface perpendicular, to the vibrating disc. 



./.The text abridged for Nature by Prof. E. W. Blake, of Brown 

 University, from a paper in the American youmal for }u\y. The illustra- 

 tions (except mirror) from photos supplied by Trof. Blake. 



A heliostat sends a beam of sunlight horizontally through a 

 small circular opening. This beam passes into a dark closet, 

 and at a distance of several feet from the circular opening falls 

 upon the mirror above described, placed with its axis inclined 

 45° to the horizon. The rays, reflected vertically downward, 

 pass through a lens at whose focus they form an intensely 

 luminous image of the circular opening. 



