August, igo6.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



499 



The camera is always held in the hand, and pointed 

 in a direction which, as a rule, is well away from that 

 of the sun. 



If the reader examines the two plates of photographs 

 he will see that good details arc given both in the heavy 

 cumuli (Plate i.. Figs, i, 2, and 3), and in the light, 

 fleecy clouds (Plate i, Figs. 4 and 5, and Plate 2, Figs. 

 I, 4, and s). It may be considered that the contrast 

 between the blue sky and cloud, in some of the illus- 

 trations, such as Plate i, Fig. 2, is too strong; from a 

 pictorial point of view, this is possibly true, but 

 from the cloud-form standpoint, I do not think it is 

 e.xcessive. 



Very interesting is the photograph in Plate 2, Fig. 5 

 On the occasion on which this plate was exposed, there 

 were cross currents in the upper air, and the apparent 

 mingling of the clouds formed a striking object. In 

 the same plate (Fig. 3) the photograph illustrates an 

 overcast sky, with low clouds travelling quickly from 

 north-east. Fig. i, also in Plate 2, is a good illustra- 

 tion of clouds being drawn out by the action of a, faster 

 moving current of air. The form known as " mare's 

 tails," is well sho'wn in Piatt- i, Fig. 4, while Fig. 5 

 of the same plate, is typical of " mackerel sky." 



Most of these photographs were secured during 

 spare moments, generally between i and 2 o'clock, p.m., 

 so that the best positions or conditions of the clouds 

 could not always be chosen. The fact also that they 

 were taken at .South Kensington indicates further that 

 the London photographer need not necessarily go far 

 afield to find his subjects. 



The Dipping R^efractometer. 



\Vk have received from Mes.srs. Carl Zeiss a docriplinn of 

 their latest fonn of dipping refraclomclcr, together with a 

 bibliogiaphy of papers in scientilic literature dealing with 

 the .subject. The dividing line between (jhysics antl 

 chemistry is being gradually broken down, .-ind wa are be- 

 ginning to trace a relationship between iluiiiic;d constitu- 

 tion and physical characteristics. The determination o! 

 many physical data has become of recognised value iji 

 chemical analysis, and this is notably the case with the 

 refractive index, which is of considerable use as a rapid 

 sorting test, especially in the analysis of oils and fats. The 

 firm of Zeiss has made a special instrument, known as the 

 butyro-rcfractometer, for this purpose, and this is in com- 

 mon use in laboratories all over the world. The dijiping 

 refraetometer, which is intended for the examination of 

 liquids in general, is not so well known, though in many 

 instances it will give immediate results as accurate as those 

 given by chemical methods. The prism and plate are 

 formed from one piece of glass, which is to be immersed in 

 the given liquid, and the degree of the refraction of the light 

 can then be read on the scale by means of the telescope. 

 ■J he "refraction is proportional to the amount of the sub- 

 stance in the solution, and it is thus possible, with (he aid 

 of special tables, to make rapid determinations of, say, the 

 amount of alcohol in spirit, albumen in blood serum, sugar 

 in extracts, or to determine the strength of solutions of 

 various salts in water. 



The San Francisco Earthquake. 



.V Co.M.Missio.N to consider the Californian earthquake was 

 appointed three days after its occurrence, and with the same 

 .\nierican promptness has already presented its preliminary 

 report. From it we gather that the area of destructive 

 I iTects extended over four hundred and fifty square miles of 

 territory, and was distributed on either side of a great rift 

 extending for a distance of some hundred and eighty-five 

 miles. Along the hundred and eigfity-five miles of this 

 rift, where movement has actually been observed, the dis- 

 placement has been chiefly horizontal, and the country S.W. 

 of the rift has moved to the N.W. relatively to the country 

 Oil the other side of the rift. The amount of dislocation 

 varies in the neighbourhood of the rift. Sometimes it is 

 not more than six feet, sometimes as much as sixteen feet ; 

 iiL,dit or ten feet is the average. There w-as also a slight 

 Nirlic.d nuntinent amounting in some places along the rift 



Signature of the San Francisco Eartliquuke, 



iVrllten bj/ mtam of Ihe seismograph at Oaklaiul, Calijurnia. 



t(. four feet. It is the great length of the rift which makes 

 the e.uthquake unique. Within the area of destructive 

 effects the intensity varied greatly. It was greatest on the 

 rift line. W'aler-p'ipes, conduits, and bridges crossing the 

 line were rent asunder ; trees were uprooted and cast to the 

 ground in great numbers, and others were split from the 

 roots up ; some were snapped olT short. Buildings were 

 usually wrecked, but some escaped with slight damage. 

 I'issur'cs opened in the earth and closed again, and in one 

 case a cow was engulfed. The places which sulTered most, 

 like San Jose, Stanford University (seven miles from the 

 rift), are those which are underlain to a great extent by 

 loose geological formations. It is suggested that the origin 

 of disturbance lay at a considerable depth. A curious fact 

 mentioned, however, by a correspondent of the Scientific 

 American is that in the .Mniadan quicksilver mines of San 

 [os^, 1,500 feet deep, the workmen did not feel the shock, 

 though the buildings at the mouth of the mine were shaken 

 down. 



