August, 1912. 



KNOWLEDGE. 



If we were to measure the strength by the area 

 disturbed, the Kangra earthquake would have to 

 be regarded as among the greatest of all recorded 

 earthquakes, as superior to the Japanese earthquake 

 of 1891, as roughly equal to the Assam earthquake 

 of 1897, 3'et as inferior to the much less disastrous 

 earthquake of Charleston in 1886. The extent of 

 the area of complete destruction is a more trust- 

 worthy standard. Measured in this way, the 

 Kangra earthquake falls far short of the Assam 

 earthcjuake of 1897. The most satisfactory test 

 of all, however, is the intensity of the shock within 

 the central area, but this is known preciselj' in 

 the case of onh' a few recent earthquakes. At 

 Dharmsala, the shock was distinctly stronger than 

 the Californian earthquake at San Francisco in 

 1906 or the Calabro-Sicilian earthquake at Messina 

 in 1908. At Kangra it was nearly twice as strong 

 as at either of these places. But, even at Kangra, 

 the intensity was less than that of the Japanese 

 earthquake of 1891 in the Mino-Owari plain, and 

 was not to be compared with that of the same 

 earthquake in the crushed and distorted rocks of 

 the Neo Valley. 



In its destructive effects, the Kangra earthquake 

 reiterates the lesson which governments are so slow 

 in learning. Thickness of wall alone is no safe- 

 guard ; it ma\- be a source of weakness. With 

 inferior material and no frame-bindings, such a 

 mass is at once shattered by an earthquake shock, 

 as in the barracks at Dharmsala, where many Ghurka 

 soldiers were killed and wounded. In the Kangra 

 valley, ordinar\- buildings had walls of mud or rubble 

 masonry surmounted by a heavy slate roof. Few 

 structures could offer less resistance to an earth- 

 quake, the result being that more than a hundred 

 thousand houses were destroyed in Kangra and the 

 surrounding country. Mr. Middlemiss considers 

 that it would be useless to urge the construction 

 of earthquake-proof houses or to discountenance 

 building on ridges or mountain-spurs. Disastrous 

 earthquakes, he remarks, are isolated occurrences, 

 and it is economical to make use of materials close 

 at hand, and convenient to follow familiar styles 

 of building. But the government that urged such 

 reasons for inaction might with equal justice neglect 

 to insure their property against tire, or to prepare for 

 a foreign war. 



THE OPTICAL CONVENTION, 1912. 



This convention was held in the Science Museum, South 

 Kensington, from June 19th to the 26th, under the presidency 

 of Professor Silvanus P. Thompson, D.Sc, F.K.S. 



The objects of the conference were to investigate how theory 

 can further industrial development, and how practical problems 

 may direct theoretical investigation ; to discuss the better 

 organisation of the British optical industry, and the improve- 

 ment ot British optical manufactures ; and to ascertain and 

 make known existing wants and deficiencies. The exhibition 

 held in connection with the conference was designed to show 

 the resources of British manufacturers of optical appliances. 



Messrs. Reynolds & Branson, Ltd., exhibited a special 

 adjustable front stage for the Stroud & Rendell optical lantern, 

 which enables an ordinary microscope, with the eyepiece 

 removed, to be used for projection. 



A new type of sunshine recorder was shown by the Cambridge 

 Scientific Instrument Company — Callendar's Bolometric Sun- 

 shine Receiver. This consists of two platinum resistances 

 mounted on a mica framework, hermetically sealed up in a 

 glass bulb filled with dry air. One of the resistances is 

 blackened, the other is left bright The two are connected in 

 the opposite arms of a recording W'heatstone Bridge. When 

 radiant heat falls on the receiver, the blackened resistance 

 absorbs more heat than the other, its temperature rises and 

 the recorder is thrown out of balance. On the; usual clock- 

 driven drum these variations are marked, indicating not only 

 the number of hours of sunshine, but also the intensity of the 

 radiation in absolute units. 



The same firm also showed an improved form of Thomson 

 Galvanometer invented by Professor Paschen, which is many 

 times more sensitive than the normal form. 



Mr. K. W. Munro has designed an anemograph which 

 records, on a single chart, wind pressure, as well as direction 

 and time. This should replace the expensive double instru- 

 ment at present employed. 



Messrs. Raphaels, Ltd., have evolved handy instruments for 

 measuring any muscular imbalance of the eyes in the Maddox 

 Near Vision Phorometer and in the Micro-telescope, a useful 

 combination of the telescope and microscope giving magnifica- 

 tions of 12 and 20 diameters respectively. 



A very interesting loan collection was also on view, including 

 a Star- Photograph Micrometer, many early types of micro- 

 scopes, a camera lucida formerly belonging to Dr. Wollaston, 

 a little Dumpy Reflector Telescope made by James Watson 

 in 1794 of very perfect figure with both Gregorian and 

 Cassegrain, an original Nicol Prism by William Nicol and 

 one of Fraunhofer's prisms. 



The catalogue will be useful as a record of the various types 

 of instruments made by British manufacturers in the different 

 branches of optical science. u u p 



Among the papers read at the recent Optical Convention 

 there are some which are of considerable interest to the 

 general public, who are not, as a rule, concerned with the 

 manufacture or use of optical instruments other than the eye 

 and spectacles. Dr. M. von Rohr, of the Zeiss works at Jena, 

 dealt with the form of spectacle lenses designed to give a field 

 of " direct vision": in other words to enable the wearer of the 

 glasses to transfer his gaze from one object to another by 

 simply rolling his eyes without moving his head, and this 

 without any loss of distinctness of vision. Another paper by 

 Messrs. Dow and .Mackinney on " Some Recent Advances in 

 the measurement of light and illumination " describes some 

 methods which should help to popularize such measurements. 

 Thus, in choosing a wallpaper for the drawing room, we 

 should not allow ourselves to be content with a surface bright- 

 ness of less than 0-3 foot candles. For the library or the 

 dining room we may be prepared to accept very much less 

 than this. If we provide ourselves with a holophane lumeter 

 and a celluloid test-card, we can easily discover whether the 

 samples of wallpapers submitted to us by the builder come up 

 to our standard. A paper on the design and construction of 

 large Polariscopes by Professors Coker and S. P. Thompson, 

 will be of interest to those who saw, at a recent Soiree of the 

 Royal Society, the wonderful double-refracting effects produced 

 by varying stresses in certain celluloid models. A paper on 

 errors of observation by Messrs. Baker and Bryan will be of 

 interest to naval officers and all who make use of the sextant 

 and prismatic compass. „, .^ .. 



