May 4, 1893] 



NATURE 



13 



(Moniteur de la Photogr.). A series of twenty-four pages is 

 arranged, the first having a clear grey tint, the second one of 

 double intensity, and so on to the twenty-fourth, the tint of 

 which is nearly black, being twenty-four times more intense 

 than that of page I. On each page are printed a few phrases 

 in black letters of different sizes. In a badly lit room one 

 may estimate the amount of illumination by turning over the 

 leaves of this little book, held about a foot from the eyes, until 

 one can no longer read the line of letters of a selected size. 

 With good illumination you may proceed to the twentieth or 

 twenty-fourth page, but with poorer light you may be stopped 

 at the tenth, or twelfth, or fifteenth. The instrument is for 

 indoor use exclusively. In schools it might prove useful in 

 testing the vision of children. 



A PERIODICAL which will show what natives of India can do 

 in some branches of science has been started in Bombay. It 

 is called The Indian Medico- Chirurgical Review, and is edited 

 by N. A. Choksy. We have received the third number, in 

 which several native writers" record the results of original 

 observation, while there are many good notes on work being 

 done in Europe. In one article the Review urges the necessity 

 for the establishment of a teaching university in Bombay. As 

 the teaching of law, medicine, and science in the presidency 

 is practically located in the city of Bombay, and hence in touch 

 with the existing examining University, a few professorships 

 might, the Revieiv thinks, be endowed, and eminent men 

 invited from Europe to occupy the new chairs. The Reviciv 

 also suggests that the Government might with advantage 

 "copy the system of the German Universities by establishing 

 biological, physiological, pathological, bacteriological, and 

 hygienic institutes, in connection with these professorships, and 

 place over them professors who would go on teaching and at 

 the sam; time carry on original researches." 



In the report of the Geological Survey of India for 1892 

 reference is made to Dr. Noetling's visit to the amber and jade 

 mines of Upper Burma — a visit which was rendered possible by 

 the starting of the Maingkwan column. The so-called amber 

 turns out to be a new variety of this form of fossil resin, to which 

 the name of Burmitehas been assigned by Dr. Noelling in con- 

 junction with Dr. Otto Helm (a distinguished authority in this 

 line) of Danzig, to whom specimens were forwarded. The 

 peculiarity of Burmite is a fluorescence, giving the mineral an 

 appearance as of solidified kerosineoil : and, as far as has yet 

 been seen, it is of darker colours than is usual with amber 

 proper (succinite) ; while it is a little harder than the latter. The 

 colour alone is, according to the present fashion in Europe, 

 against the mineral, but some of the darker varieties of brown 

 red colour, present on being cut deeply en cabochon, the flat or 

 under face being turned to the observer, a really gorgeous ruby 

 tint which should make the stone desirable ornamentally. The 

 so-called jade— for the actual constitution of the mineral as 

 worked in Burma determines it properly as jadeile — is worked 

 by pit and quarry mines, the former for forty miles along the 

 bank of the Uru river southwards from Sankha, while the latter 

 are excavated on the top of a plateau at Tammaw, eight miles 

 out of Sankha, in the Mogoung subdivision. The industry seems 

 to be a thriving one, and rather promising for future more 

 systematic and skilled development, for at least 500 men are 

 engaged every season in working the quarries. White is the 

 commonest colour, the green varieties being of much rarer 

 occurrence ; while, in some of the fewer boulders obtained from 

 the laterite beds along the course of the Uru river, a " red 

 jade " appears to have been produced by ferruginous decompo- 

 sition change. 



There are two stations in Italy for the economic investiga- 

 tion of the diseases of plants ; one at Pavia, established in 



NO. T227, vol. ^8] 



1871 in connection with the Botanical Institute of the Royal 

 University, and now under the directorship of Prof. Briosi ; 

 the other at Rome, established in 1887, and presided over by 

 Prof. Cuboni. They are required to investigate the nature 

 and cause of diseases, to test and provide remedies, and to 

 disseminate information by lectures and publications. As might 

 be expected, the diseases of the vine and of the olive occupy a 

 large share of their attention. 



Prof. V. Dvorak, of Agram, uses a very simple apparatus 

 for demonstrating the oscillation of the air in sound phenomena. 

 In an ordinary resonating sphere the short neck is replaced by 

 a small metal plate with a conical hole opening inwards, its 

 shortest diameter being about 2 mm. When the resonator sounds, 

 the passage of air through the hole is strong enough to extinguish 

 a lighted match. If a small paper wheel resembling a water- 

 wheel is placed a little below the opening and the resonator stands 

 about 3 cm. in front of a wall, the blowing of a horn, or the 

 singing of the proper note, is capable of setting the wheel 

 in rapid rotation. A very serviceable lecture apparatus for 

 measuring the intensity of sound is illustrated in the Zeilschrijt 

 fiir Physikalischen Unterricht. A narrow glass tube bent at a 

 very obtuse angle is half filled with alcohol. One end of the 

 tube has a conical opening, and this is placed at a distance of 0'5 

 cm. from the opening of the resonator described. The whole is 

 mounted on a board capable of adjustment to any angle. The 

 puffs emitted from the resonator when responding to a sound 

 affect the level of the alcohol, and the displacements are read of! 

 on a scale attached to the tube, projected, if necessary, on to a 

 screen. Another effect of sound easily observed is that of 

 repulsion. A light resonator of the ordinary construction is 

 floated on water, its axis being kept horizontal by means of an 

 attached piece of wire. On blowing the horn, the sphere will 

 float in the direction opposite to that in which the neck is 

 pointed. To produce continuous rotation, four resonators are 

 attached to a light cross of wood turning on a needle point, or 

 one resonator with four bent necks is suspended by a thread. If 

 this acoustical reaction wheel is placed in one corner of the 

 lecture theatre, it can be set rotating from the opposite corner by 

 a strong tuning fork, or even by singing through a conical tube. 



At the recent exhibition of the Societe Fran9aise de Physique, 

 M. Hurmuzescu showed the following experiment : — A metallic 

 wire, through which a continuous current is passed, is stretched 

 horizontally in a glass tube containing gas either at the ordinary 

 atmospheric pressure or rarefied. As soon as the wire becomes 

 red-hot it begins to vibrate in a vertical plane, and the contain- 

 ing tube becomes much hotter at the bottom than at the sides. 

 This effect has not been satisfactorily explained by its dis- 

 coverer. 



M. Claude showed at the same exhibition, an instrument for 

 measuring the difference in phase between the current in a 

 circuit and the impressed electromotive force. The principle of 

 the instrument is as follows : — When a piece of soft iron, fixed to 

 the end of a spring, is placed before the pole of an electro- 

 magnet having a permanently magnetised core and traversed by 

 an alternating current, it is attracted and vibrates with the same 

 period as the current. If the spring also carries a mirror from 

 which a ray of light is reflected on to a scale, the length of the 

 band of light produced will be proportional to the maximum 

 displacement of the mirror. Two such electromagnets are used, 

 acting on the piece of soft iron in opposite directions, and at 

 such distances that they produce the same maximum deflection, 

 one magnet being placed in series with the circuit, and the other 

 joined to the ends of a non-inductive resistance. Under these 

 conditions the length of the band of light is proportional to the 

 cosine of half the angle of lag. 



