424 



NA TURE 



[March 6, 1902 



When this is done, a telescope is employed to photoRraph the 

 region about the zenith as reflected from the upper surface of 

 the silvered mirror. In this position the photographic telescope 

 will lie in the same direction as the fixed collimator, and thus it 

 can be arranged to have a suitable exposing screen, by which, 

 at any instant, a short exposure is given to a strong light 

 placed near the collimator slit, which will give an image of the 

 slit superposed on the region near the zenith, the centre of this 

 image indicating the instrumental zenith. All that remains to 

 be done is to provide a duplicate apparatus at a second station, 

 and by operating the exposing shutters of their respective col- 

 limators by electric means, the zenith of each place will be 

 automatically recorded. The difference of longitude between 

 the two stations will be equal to the difference of the right 

 ascensions of the two collimator images. The chief corrections 

 will be owing to the possible prismatic form of the reflecting 

 mirror and the catalogue errors introduced in computing the 

 right ascensions. 



INDIAN SURVEYS.'^ 



THE Report on Indian Surveys for the year 1899-1900 is now 

 before the public, and the resolution of the Government 

 of India which concludes this report pronounces it to be one 

 which reflects great credit on the " able and effective adminis- 

 tration " of Colonel St. G. Gore, R.E., the present Surveyor- 

 General. Field operations were carried on by one double and 

 fifteen ordinary parties and four detachments. Eight of these 

 parties were employed on topographical (including geographical) 

 surveys, only one on trigonometrical work, and the remainder 

 included cadastral and traverse surveys and special geodetic 

 investigations. A large area of forest survey was also completed. 

 The total outturn amounted to nearly 150,000 square miles, of 

 which more than 120,000 square miles were "reconnaissance" 

 or geographical surveys, on the rl-inch or smaller scales, in 

 Burma and on the north-west frontier. The total area of rigorous 

 surveys on all scales was 29,418 square miles. The normal scale 

 for topographical surveys in India is i inch = I mile, and the 

 cost of these surveys (which are based on rigid triangulation) is 

 from 25 to 30 rupees per square mile — a cost which compares 

 favourably with that of American surveys conducted under 

 similar physical conditions, but with a very different staff of 

 employes. The cheapness of Indian surveys is doubtless due 

 to the general employment of skilled native labour. In this 

 connection it is satisfactory to note that natives are now being 

 instructed to triangulate and that the magnetic party which has 

 been lately inaugurated will be placed under a native observer. 



The general increase in the outturn on that of the previous 

 year is due to the accession of an unusually large area of geo- 

 graphical mapping, full details of which are not published. 

 Topography, conducted on rigorous methods, was chiefly con- 

 fined to Burma and Sind. two countries which, whilst they 

 balance each other geographically on the east and west, afiord a 

 useful contrast for comparison of cost rates and methods of 

 survey. Of the special work undertaken by the Department, 

 that which resulted in a comparison of the values of level 

 deflection by means of observed latitudes on Great Arc stations 

 receding gradu.ally from the Himalaya is most instructive, and 

 speci.al attention is called by the Government of India to Captain 

 Lenox Conyngham's discussion of the results obtained. Experi- 

 ments were made with the Bridges-Eee photo-theodolite, and 

 with the Jaderin base measuring apparatus which promises, if not 

 to supersede the complicated adjustment of compensation bars 

 altogether, at lea.st to simplify the process of measuring bases 

 for all but the most rigidly accurate geodetic purposes. The 

 former is pronounced to be a very promising auxiliary to the 

 plane table (especially in mountainous countries), " but it will 

 never supersede it." This, it may be remarked, is nearly 

 coincident with the opinion of Canadian surveyors who have 

 tested photo-topography far more exhaustively than has been 

 done in India. As regards the Jaderin apparatus, an unfortunate 

 uncertainty about the value of the coefficients of expansion in 

 the metals forming the tape has deferred an expression of 

 opinion on its success or otherwise. 



Record is made of a most useful invention in the printing 

 office by a R. E. foreman which enables the process of photo- 

 graphy to be eliminated from the cumbersome method of map 

 » General Report of the Operations of the Stirvey of India Department, 

 1899-igoo. 



NO. 1688. VOL. 65] 



reproduction by photo-zincography. There can be little doubt 

 of the value of the invention, which is fully described, 'and which 

 has been patented in India. It has already enabled the printing 

 office to deal with a vast number of maps in excess of the 

 normal outturn. We are glad to observe that the invention has 

 met with prompt recognition by the (Government of India. The 

 report contains three or four excellent photogravure illustrations, 

 one of which is a suggestive view of a railway bridge on the 

 Mandalay-Kunlon line, which is now under construction. 



The map illustration is perhaps the most unsatisfactory feature 

 in the report. One map at the commencement of the volume 

 purports to show the " progress of the Imperial surveys," and ex- 

 hibits a special colour to denote ' ' geographical reconnaissance on 

 various scales." According to this map a large area of the Madras 

 province has never even been "geographically reconnoitred" — 

 which is a very astounding fact if it is true — for it is blank white 

 paper. And the fact that no surveys are shown in Baluchistart 

 must be due either to an affectation that British Baluchistan 

 .and i^)uetla have nothing to do with India, or else it is a 

 deficiency in the illustration, for it leaves an enormous area of 

 the outturn of the Department which is included in the body of 

 the report absolutely unaccounted for. The triangulation chart 

 adjoining shows a very sati.sfactory-looking series extending to 

 Kandahar from the Indus, and another series reaching half way 

 through Makran. Triangulation usually carries topography on 

 its back, and doubtless it does so in the present instance. Why 

 the extent of transfrontier "geographical reconnaissance" (to 

 say nothing of exact detailed topography) should not be shown 

 in the chart it is difficult to imagine. 



MILROY LECTURES ON TYPHOID FEVER. 

 TN his second and third (final) lectures at the Royal College 

 •*■ of Physicians, Prof. Corfield gave detailed descriptions of 

 a number of outbreaks of typhoid fever which had been traced 

 to specific contamination of drinking water, and exhibited a 

 table which he had prepared demonstrating the fact that duriiig 

 the ten years 1S91 to 1900 (with the exception of 1S97) typhoid 

 fever has been more prev.alent in St. George's, Hanover Square, 

 in November and December than in August, September and 

 October, the months when it is norinally prevalent, the average 

 number of cases per month for November and December having 

 been 7-2, and for August, September and October only 4-2. 

 This excess of typhoid fever in November and December was 

 coincident, he said, with the increase in organic matter in the 

 water supplied by the Thames companies when the river was in 

 flood. He pointed out that Mr. Shirley Murphy, the Medical 

 Officer of Health of the London County Council, had drawn 

 attention to the fact that in 1894 there w.as an excess of typhoid 

 fever in November and December in the London districts 

 supplied by all Sthe water companies, except the East London 

 and the Kent companies, and that this followed exceptional 

 floods in the rivers Thames and Lea. Dr. Corfield stated that 

 he was satisfied from these facts that the distribution of in- 

 efficiently filtered river water during November and December 

 was the cause of the increase in the number of typhoid fever 

 cases which occurred among persons especially liable to the 

 disease. 



Among the cases of polluted well water described by him, 

 perhaps the most interesting and remarkable was one which he 

 had recently investigated at a country house where there had 

 been a case of typhoid fever, and where, by a peculiar arrange- 

 ment of the suction pipes of a pump, water was, in certain 

 circumstances, siphoned automatically from a pond polluted 

 with the house sewage into the well supplying drinking water. 



Dr. Corfield then described a number of outbreaks in which 

 the poison of typhoid fever had been distributed by means of 

 milk, oysters, cockles and mussels, ice-creams, ginger-beer, 

 and even oranges and grapes, these fruits having been thrown, 

 because they were decaying, into an ash-pit where typhoid 

 excreta had been previously put, and having been picked up 

 and eaten by a number of children. 



Among the reports quoted were some from Belgiuni, France 

 and Germany, kindly sent him by Dr. Kuborn, of Seraing-Licge, 

 Dr. Brouardel, of Paris, and Dr. Pistor, of Berlin, respectively, 

 and also some from different parts of the United States, and 

 others by Dr. J. Ashburton Thompson, the President of the 

 Board of Health of New South Wales. 



In concluding his account of the communication of the disease 



