CORRESPONDENCE. 



ORIGIN OF THE FINGER PRINT METHOD. 

 To the Editors of " Knowledge." 



Sirs, — Kindly correct an error in your February number. 

 Page 45, about Fingerprints. You quote Sir Francis Galton 

 as saying in his Reminiscences " that Sir William Herschel 

 in India had experimented with them since 1887." I do not 

 know where you got this date from, but Galton never gave it. 

 .\s a matter of fact before I left India in 1878 I had been 

 experimenting for twenty years (Galton says " many years "I, 

 and had successfully established, not only the individuality, 

 but the practical persistence of the pattern, as an unfailing 

 method of identification, before any one else had entertained 

 the idea. When I left India the system was in public use 

 with the knowledge of the Heads of the Registration Depart- 

 ment, and of Gaols, as well as for Pensioners, and in my own 

 Court, and was matter of common knowledge in Bengal. The 

 <jOvernment of Bengal had known of it from me many years 

 before 1878, as a means of preventing forgery during the 

 Indigo disputes in 1861 and 1862. 



I trust you will do me the justice to insert this letter in your 

 next number. 



I am engaged at present in arranging my records for 

 publication in facsimile by the Clarendon Press. 



W. J. HERSCHEL. 



.\ METEOR. 

 To the Editors of " Knowledge." 



Sirs. — A beautiful meteor was seen here (Sunderland. 

 February 16th I about 5.33 p.m. The head was almost as 

 bright as \'enus, but larger in appearance. It left a trail of 

 light behind it which appeared to be reddish in hue : it was 

 \isible several seconds. 



I am not an astronomer, but think that the note would 

 be of interest to vour readers. 



F. H. S. 



THE SUN'S RE\"()LL"T10N. 



To the Editors of " Knowledge." 



Sirs, — As a student of .-Vstrological lore. I sometimes draw 

 a figure for my birthday anniversary. But I find the time for 

 the sun's return to its place at birth varies from year to year. 

 For instance, at the time of my birth the sun was in Pisces 

 24-41, which occurred at 10 a.m. on March 15th, the year of 

 Hiy birth. But in 1910 the sun came to that point sixteen hours 

 later, or at about 4 a.m. on the 16th. and this year later still, \iz.. 

 about 9.30 a.m. on the 16th. Can any of your readers kindly 

 explain how it is that the sun does not return to the same 

 point in the Zodiac at the same time everv vear ? 



H. A. B. 



IS SPACE INFINITE? 



To the Editors of " Knowledge." 



Sirs, — The following extracts from Professor Pickering's 

 Article in Popular Astronomy of August last are of special 

 interest in connection with Mr. Barclay's letter on the subject 

 of the "Eternal Return." The suggestion that space is curved 

 may be welcomed by many of your readers as an alternative 

 theory to that of Laplace and others who ha%e assumed that 

 space and time are necessarily infinite. 



H. PERIAM HAWKINS. 



"Everyone who considers the question of proceeding indefinitely 

 along a straight line must feel the impossibility of coming to a point 

 where there is no space beyond him, and j'et at the same time he must 

 feel that infinite space is itself an impossibility. To avoid this difficulty 

 it has been suggested that space is curved, with a definite radius and 

 direction of curvature at every point. In other words we should accept 

 the idea that plane triangles and rectangular co-ordinates are merely a 

 close approximation to fact, but that all figures are really constructed in 

 spherical co-ordinates. 



"Now it is a properly of infinite space, of any number of dimensions, 

 that if it be properly curved, and inserted in space of one higher dimen- 

 sion, it will become finite. Thus if infinite space of one dimension, 

 represented by a straight line, be properly curved and inserted in a plane 

 it 'vill become the periphery of an ellipse ; if uniformly curved it will 

 become that of a circle. Similarly, if space of two dimensions, repre- 

 sented by a plane, be properly curved and inserted in tliree-dimensional 

 space, it will become the surface of an ellipsoid. Similarly, if ordinary 

 or three-dimensional space be properly curved, and inserted in space of 

 four dimensions, it will become finite in volume, and represent what would 

 correspond to the surface of a fourth-dimensional .solid. Thus, if we 

 .should go far enough east, we should reach the west, if far enough north 

 we should reach the south, and if far enough into the zenith we should 

 re.ach the nadir." 



" If it is difficult for us to imagine infinite space, it is still more so to 

 comprehend infinite time. As we go back eternally through the ages 

 how is it possible for there to be still an infinity of time before that ? 

 Vet we cannot conceive of an actual day or instant before which time 

 did not exist. In graphical solutions time is represented by a straight 

 line, and may be compared to space of one dimension. But suppose 

 that time, too, is curved, and has another dimension that we have not yet 

 detected. Time then may be represented by an ellipse or a circle, and if 

 we go back far enough into yesterday, we shall arrive at to-morrow. 

 Of course, we s/iould not live our lives over a^ain, because matter in the 

 ineantitne would have changed, and when the present day again arrives, 

 it will be upon a very different universe. Both infinity of time and a 

 return of time seem to us now impossible. If the latter is the more 

 difficult to comprehend, may it not be simply because it has not occurred 

 to us before ? " 



THE NEW MAP OF THE MOON. 



To the Editors of " Knowledge." 



Sirs, — Our nearest companion in space has. ever since the 

 invention of the telescope, attracted a good deal of attention. 

 Many have been the attempts to map its surface. Perhaps 

 the first re.ally useful map was that of Beer and Madler. thirty- 

 seven-and-a-quarter inches in diameter, published in 1834. those 

 previouslyissued by Hevel and Tobias Mayerbeing much behind 

 in detail, as also were those of Russell and Blunt. Lohrman's 

 work was on the same scale as Beer and Miidler's. but. owing 

 to the failure of his vision, was not completed until produced 

 under the editorship of Schmidt, some thirty years ago. In 

 1876. Xeison issued a useful book on the Moon, containing a 

 capital map two feet in diameter. But in 1878, Schmidt's great 

 map, six feet in diameter, was published, the labour of thirty-five 

 years. Since these maps were issued a new era has dawned 

 in selenography ; the telescopist is reinforced by photography. 

 The latter, whilst it misses the sharpness of telescopic vision, 

 puts detail in its accurate place. The new map has been 

 constructed from combined telescopic and photographic obser- 

 vations, on a scale of se\enty-seven inches to the moon's diameter, 

 by Mr. Walter Goodacre, the director of the Lunar Section of the 

 British Astronomical .Association. It has taken seven years 

 to accomplish this noble work. Its accuracy may be judged 

 when it is considered that it is based " mainly on 1,443 

 measured points on the lunar surface, made by Mr. S. A. 

 Saunder, ^I..A.. F.R.A.S..and pubhshed in the Memoirs of the 

 Ro^-al Astronomical Society, Volume LVII." The sketches 

 of many of the best observers, including the late Major P. B. 

 Molesworth and Mr. Gopdacre, have been used in the con- 

 struction. This monumental work, which has been exhibited 



141 



