April 24, 1891.] 



SCIENCE. 



229 



from 13 to 50 miles. In the hot season the velocity was less than in 

 the cold (38 miles against 33 miles). It was least in the early morn- 

 ing, then increased, at first slowly, then faster, reaching a maxi- 

 mum between 9 and 10 p.m. Thunder-storms travel most quickly 

 from south-west, west, and nortli-west. An interesting geographi- 

 cal difference was observed. From west to east the velocity in- 

 creased at first; but about 30" to 35° east longitude a maximum 

 was reached, and farther east the speed declined; the decline 

 showing, however, a secondary maximum between 45° and 50°. 



— With reference to observed changes in the earth's axis of ro- 

 tation, says Nature, it has been pointed out that through changes 

 in distribution of air-pressure and movement of water-masses, 

 considerably differences of level in the ocean may be produced. 

 Herr Lamp notes the displacement northwards of the maxima of 

 air-pressure in the trade-wind region, and of ocean-currents, as 

 the sun rises in summer. Thus a certain quantity of water passes 

 over in summer from tlie southern to the northern hemisphere; 

 and it is improbable that compensation takes place by means of 

 undercurrents. As the year advances, water passes back to the 

 southern hemisphere, reaching there a maximum in our winter. 

 This periodical transferrence of mass is supposed to cause periodi- 

 cal variation in the earth's axis. Herr Lamp calculates that to 

 cause a change of latitude of 0.5", it would be sufficient, that, at 

 180° longitude from Berlin, a water-mass of 3,500 cubic metres 

 should move in a meridional direction from 30° south latitude to 

 35° north latitude; and that, with reference to the oceanic area 

 concerned, we need only suppose a mean elevation of 10 centime- 

 tres (or 4 inches) in the sea level. 



— The annual report of the Berlin branch of the German Mete- 

 orological Society contains the results of rainfall observations at a 

 number of stations in and near Berlin for the year 1890. This 

 year is among the dryest experienced since 1848, when regular 

 observations were begun. The mouths of February and Septem- 

 ber, especially, are the dryest on record. Dr. Hellmann, the secre- 

 tary, has carried on some useful experiments to determine the 

 influence of the height of rain-gauges upon the records of rainfall, 

 — a matter of considerable importance in towns, owing to the 

 ■difficulty of obtaining a good exposure at a low level. He finds, 

 according to Nature of April 3, that about a quarter of the rain- 

 fall is lost in an elevated exposure, such as on the roof of a house, 

 during strong winds; but he arrives at the important conclu- 

 sion that an elevated exposure is permissible if the gauge can be 

 protected from the disturbing influence of the wind. The re- 

 port also contains a list of the severe winters since 1738. The 

 coldest winter was 1788. On Dec. 28 a minimum of —31.6° was 

 recorded. 



— A new method has been devised and patented in England for 

 ascertaining the requisite time of exposure in photography. An 

 instrument for measuring the relative intensity of the photo- 

 graphically active rays reflected from any landscape or other ob- 

 ject by observing the time required for the light from a phos- 

 phorescent compound to fade from its maximum intensity to the 

 intensity of the light reflected from the object, is employed. It 

 consists, accoi-ding to The Engineering and Mining Journal, of 

 an opaque tube with an eye-piece at one end ; while at the other 

 is a plate of glass, part of which is coated with Balmain's paint, 

 or some similar phosphorescent substance emitting only rays 

 which act upon an ordinai-y photographic plate. The paint must 

 either he opaque, or must be made opaque by means of a backing. 

 Behind this glass is a piece of ground-glass, and there may also 

 be a piece of blue glass cutting off from the light reflected from 

 the object all rays except those which act on a photographic 

 plate. The frame carrying these glasses is bingei, so that it can 

 be turned back in order to expose the phosphorescent substance 

 to light. When a measurement is to be made, the frame is turned 

 back and the phosphorescent surface is exposed to daylight, or 

 to the light from burning magnesium, for a time sufficient to ex- 

 cite the maximum luminosity. It is then put back in position, 

 and the apparatus is at once directed toward the object to be pho- 

 tographed. The light reflected from this object passes through 

 the unobstructed portion of the ground-glass and blue glass, and 

 at first appears dark as compared with the light from the phos- 



phorescent surface. The brightness of the latter, however, grad- 

 ually fades, until the two lights are equal in intensity. The time 

 required for this to take place is observed, and, with this datum 

 and a series of tables supplied with the instrument, the exposure 

 necessary to obtain a good photograph of the object in question 

 is ascertained. 



— Steps are being taken in Paris to prepare the way for the 

 holding of an international colonial exhibition next year on the 

 Champ de Mars. According to the Paris correspondent of the 

 London Times, the sections would be geographical, not political ; 

 all the West Indies, for instance, forming one section, all India 

 another, and so on. Specimens of all the native populations 

 would be brought over and housed as at their homes, and two 

 congresses — a colonial and an ethnographical — would be held. 



— The mineral hornblende has been artificially reproduced in 

 well-formed crystals by M. Klroustchoff, and an account of his 

 experiments is communicated to Comptes Rendus, an extract from 

 which appeared in Nature of April 9. The last few years have 

 been most fruitful in mineral syntheses; so much so, indeed, that 

 there remain very few of the more commonly occurring rock- 

 forming minerals which have not been artificially prepared in the 

 laboratory. M. Kroustchoff, who not long ago described a mode 

 of preparing most perfect crystals of quartz, has made many at- 

 tempts to reproduce hornblende, and has at length succeeded by 

 the adoption of the following somewhat remarkable process. This 

 process essentially consists in digesting together for a long period 

 of time, in vacuo, and at a high temperature, the various oxides 

 contained in natural homblendic amphiboles, in presence of 

 water. Small flasks of green glass were employed, each of which 

 was exhausted by means of a Sprengel pump after the introduc- 

 tion of the substances to be digested together. The ingredients 

 digested consisted of (1) a dialyzed three-per-cent aqueous solu- 

 tion of silica ; (3) an aqueous solution of alumina obtained by 

 dissolving aluminum hydrate in an aqueous solution of aluminum 

 chloride, and subjecting the solution to dialysis; (3) an aqueous 

 solution of ferric oxide obtained by the addition of ammonium 

 carbonate to ferric chloride in such quantity as to redissolve the 

 precipitate first formed, and dialyziug the solution ; (4) carefully 

 prepared pure ferrous hydrate; (5) lime-water; (6) freshly pre- 

 cipitated hydrate of magnesia; and (7) a few drops of caustic 

 soda and potash. The mixture presented tlie appearance of a 

 gelatinous mud. The exhausted and sealed flasks were placed in 

 a specially constructed iron many-chambered furnace, a-.id lipated 

 for three months to a temperature of 550° C. At the expiration 

 of this time the appearance of the contents had entirely changed, 

 having become much darker in color; and distributed throughout 

 were numerous brilliant little crystals, almost black in color, and 

 reminding one forcibly of natural hornblende. On systematic ex- 

 amination, they were found to consist of flattened prisms 

 identical in character with hornblende. Under the micro- 

 scope they exhibited the hornblendio yellowish-green color and 

 pleochroism. Their index of refraction was the same as that of 

 natural hornblende, about 1.65. The angle between their optic 

 axes was found to be 82° : that of natural crystals varies from 

 80° to 85°. Analyses gave the characteristic amphibolic percen- 

 tages, that of SiOo being 43.3. In addition to these crystals of 

 hornblende, it is interesting to note that pyroxenic crystals re- 

 sembling those of the augite family were also found in the flasks, 

 together with crystals of a zeolite and of a variety of orthoclase 

 felspar; and, finally, some exquisite little ciuartz crystals were 

 observed, showing cavities containing liquids and bubbles resem- 

 bling those of natural rock crystals. 



— Welch, Fracker Company, New York, have in preparation 

 '•Ohio in Art," by Francis C. Sessions, president of the Ohio 

 Archseological and Historical Society, to be illustrated with etch- 

 ings, photogravures, and many smaller cuts, reproduced from the 

 most notable works of Ohio artists. Among these may be named 

 Otto H. Bacher, James Beard, W. H. Beard, Robert Blum, Theo. 

 E. Butler, Thomas Cole, Kenyon Cox, Charles C. Ciirran, .John J. 

 Enneking. C. H. Eaton, E. Peixotto, Hiram Powers. J. H. Twacht- 

 man, Edgar M. Ward, J. Quincy Ward; to be sold by subscrip- 

 tion only. 



