P December i, 1892] 



NATURE 



13 



with their centres. In the zero position the spheres are at a dis- 

 tance of 3"icm., this being a little less than the distance of 

 maximum attraction. The deflections are indicated by those of 

 a mirror carried by a thin glass rod attached to the curved arm 

 below, and the motion is damped by a vane immersed in some 

 vegetable oil. The tangents of the angle of deflection are pro- 

 portional to the diflferences of potential to within o "9 per cent., 

 between the scale readings 0*05 and 0*4. The instrument is 

 best adapted to potentials ranging from 6000 to 60,000 volts, but 

 with potentials above 3S,ooo it is best to immerse it entirely in 

 oil. 



An account of a series of experiments to determine the tem- 

 perature of the flame of water-gas is given by Mr. E. Blass, of 

 Essen, in Stahl ttnd Eisen. The instruments employed were 

 Wyborgh's air pyrometer, Chatelier's electric pyrometer, Hart- 

 mann and Braun's telephonic pyrometer, and others by Siemens, 

 Seeger, and Ducretel. It was found that Chatelier's formula 

 for the variation of the specific heat of water vapour and other 

 gases at high temperatures was practically reliable. The tem- 

 peratures of combustion were taken for various proportions of 

 air and gas, beginning with a large excess of the latter. With 

 o*i8 cubic metres of air to one of gas, the temperature was 

 425° C. Calculated according to the old formula this would 

 have been 521. Allowing for variation of specific heat, the 

 theoretical value becomes 409. For 0714 of air, the tempera- 

 ture was 1 1 70, for 4 "1 8 it was I2i8, for 979 it was 655, and for 

 the proportion of air just sufficient for combustion the flame 

 temperature was 1169°, 



A NEW "shortened telescope," constructed by Dr. R. Stein- 

 heil, is described in the Zeitschr. fiir Instr. for November. The 

 principle resembles that adopted by Dallmeyer and Dr. A. Stein- 

 heil in their telephotographic objectives. A negative system is 

 introduced between the object-glass and the eye-piece, thus in 

 creasing its equivalent focal length. If a be the focal length of 

 the objective by itself, r its distance from the negative lens, and 

 the magnification vi times that produced without the negative 

 lens, the total length of the tube is given by l=r-\-m (a -r). 

 In a telescope actually constructed on this system, the object- 

 glass had a focal length of i6'2 cm. Its distance from the 

 nearest surface of the negative lens was 12 cm., the equivalent 

 focal length 608 cm., and the total length 27-8 cm. Hence the 

 magnification was 3 75 times that obtained by using the objec- 

 tive alone. In this case, then, a magnification of 22 diameters 

 was obtained with an effective aperture of 4 cm., a total length 

 of 27'8 cm., and a one-inch eye-piece. If the same magnification 

 and illumination had to be obtained by a long-focus objective, 

 the length would have to be 6- 8 cm. Thus the length is reduced 

 by more than one-half without the usual disadvantages of short 

 telescopes and eye-pieces of high power. 



According to a writer in the Pioneer Mail of Allahabad, 

 the thatch on Burmese houses gives a tempting shelter to snakes, 

 especially during the rains, and many of the occupants of the 

 houses would be surprised if they knew the number of snakes 

 that share the shelter of their roof on a rainy night. One night 

 an officer was wakened up by a noise in his room ; and by the 

 light of a lighted wick, floating in a tumbler of oil, he made out 

 that two combatants were disputing the possession of the small 

 space in the centre of the bedroom. The belligerents turned 

 out to be a snake and a rat, that somehow had jostled against 

 each other in the tiny tenement. 



A^VALUABLE report on the geology of north-eastern Alabama 



and adjacent portions o Georgia and Tennessee, by C. Wil- 



lard Hayes, has been published as a Bulletin of the U.S. 



Geological Survey. Mr. Hayes explains that in writing the 



NO. I 205. VOL. 47I 



report he has tried to keep it as free as possible from technical 

 terms, and, without sacrificing scientific accuracy, to present 

 the facts in such a way as to make them intelligible to the 

 largest possible number of readers in the region under con- 

 sideration. Many details which would be of interest to the 

 geologist have been purposely omitted, and only those which 

 were considered essential are given. It is expected that the 

 atlas sheets covering this region will shortly be published by 

 the U. S. Geological Survey, and supply the details to those 

 specially interested which are omitted from the report. 



A SECOND edition of Prof. Oliver J. Lodge's " Modem Views 

 of Electricity " has been published by Messrs. Macmillan and 

 Co. A new chapter on recent progress has been added. 



A VOLUME on "The Pharmacy and Poison Laws of the 

 United Kingdom " has been issued from the office of The Chemist 

 and Druggist. It contains also a brief account of the pharmacy 

 laws in force in Australasia, Canada, and Cape Colony. 



Mr. Charles E. Munroe, Torpedo Station, Newport, 

 Rhode Island, U.S.A., has completed the manuscript of the 

 second part of his index to the literature of explosives. The 

 first part was issued in 1886. The second will be issued in 

 pamphlet form if an adequate number of subscriptions is 

 obtained. 



Messrs. Friedlander and Son, Berlin, send us the latest 

 of their lists of the books which they offer for sale. It is a list 

 of works relating to ornithology. 



Penta-iodide and penta-bromide of caesium, together with 

 several other penta-halogen compounds of the metals of the 

 alkalies containing mixed halogens, have been isolated by Messrs. 

 Wells and Wheeler, and are described by them in the current 

 number of the ZeitschriftfUrAnorganische Chemie.Qx%i\xm penta- 

 iodide, Csis, is obtained in an impure form when the crystals of 

 the tri-iodide of caesium, Cslj, previously obtained by Prof. 

 Wells and described in our note of February last, vol. xlv. p, 

 325, is treated with hot water, or when solid iodine is treated 

 with a hot solution of caesium iodide. Either of these processes 

 produce it in the form of a black liquid, which solidifies in the 

 neighbourhood of 73°. The tri-iodide of caesium, moreover, 

 which is only sparingly soluble in alcohol, is found to be much 

 more readily soluble when a quantity of iodine, corresponding to 

 two atoms for each molecule of the tri-iodide, is added. Upon 

 cooling, crystals of the penta-iodide of caesium are deposited. 

 Remarkably well-formed crystals are obtained upon evaporation 

 of a more dilute solution over oil of vitriol. The crystals are 

 black and the faces extremely brilliant ; they sometimes attain a 

 diameter of a centimetre. They belong to the triclinic sys- 

 tem according to Prof. Penfield, by whom they have been 

 measured. They are at once distinguished from crystals of 

 iodine by their form and brittleness. They melt at about 73°. 

 When exposed to the air they lose iodine about as rapidly as 

 crystals of free iodine. These crystals are anhydrous, and yield 

 analytical numbers agreeing with the formula Cslj, The penta- 

 bromide of caesium may be similarly obtained by agitating a 

 concentrated solution of caesium bromide with a large excess of 

 bromine. When such a mixture is allowed to stand at a low 

 temperature the excess of bromine slowly evaporates and the 

 penta-bromide separates in the form of a dark red solid substance. 

 Caesium penta-bromide CsBrj, is a very unstable substance, 

 losing bromine rapidly at the ordinary temperature. Anothe 

 interesting compound is caesium tetrachloriodide, CSCI4I, which 

 was obtained by dissolving forty grams of caesium chloride in 

 mixture of six hundred cubic centimetres of water and two bun. 

 dred cubic centimetres of concentrated hydrochloric acid, adding 



