April 1 6, 1885] 



NA TURE 



553 



Mean 



52-5 



55'° 55'0 



* Mean or value of greatest frequency. 



Mr. Guppy's figures are too few in number, and too irregular 

 in their relation to each other and to the columns of figures on 

 either side of them, to be accepted as representative of the range 

 of vision of the Solomon Islanders, and he must have stumhled 

 on some of the better examples, or else the short-sighted men 

 have not presented themselves to him for examination. Never- 

 theless, taking the figures as they stand, they give no support to 

 the belief that savages possess better sight than civilised peoples. 

 Mr. Guppy gives 60 feet as the distance at which the test-dots 

 were distinguished, but the average of his figures is 57-5 feet, or 

 only half a foot more than Prof. Longmore worked out, from 

 observations on British recruits, as the distance which the test- 

 dots ought to be seen in good daylight. Judging from the run 

 of the figures, I should place the so-called " normal " vision of the 

 Solomon Islanders at 55 feet, or possibly at 52^5 feet, like the 

 English labouring classes of the age of twenty-one years, as our 

 figures representing that age are remarkably uniform in their 

 distribution, and therefore near the truth. The average of 

 the Solomon Islanders is, it is true, higher by 5 feet than 

 the English in my table ; but this is obviously due to the 

 absence of observations on the less perfect-sighted individuals 

 belonging to the former race. Even when the test is one of 

 seeing objects at the greatest distance, the best savages are in- 

 ferior to the best English by about one-third. Mr. Guppy evidently 

 believes that the Solomon Islanders possess very superior sight 

 compared with ourselves, especially for distant object ; and Mr. 

 J. A. Duffield, who read a paper recently, at the Anthropological 

 Institute, on the natives of some adjoining islands, was still 

 more firmly of this opinion ; but it is obvious that the question 

 cannot be decided by general impressions, nor by the result of 

 comparisons with sight the value of which we are ignorant. 

 Travellers naturally record cases in which their own sight (which 

 they believe to be good, but which may be very bad) is out- 

 stripped by savages, but do not encumber their pages with 

 negative evidence of the kind. Their mistake lies in confounding 

 acuteness of vision with the results of special training or educa- 

 tion of the faculty of seeing — results quite as much dependent 

 on mental training as on the use of the eyes. 



Bolton Row, Mayfair, April 13 Charles Roberts 



Far-sightedness 

 Allow me to corroborate the report of your correspondent, 

 whose letter appears in Nature of April 2 (p. 5 6) as 

 to the visibility of very distant terrestrial object-. In the 

 spring of 1837 I was travelling from Rome, northwards, by 

 " Vetturino," and from the summit of the Apennine on the road 

 between Florence and Bologne, I saw, with astonishment, the 

 whole range of the Swiss Alps, not merely distinguishable but 

 conspicuous. Measured on the map in a direct line the nearest 



part of the range was distant about 200 miles. The extreme 

 portions, including Mont Blanc, were considerably more. I 

 have no doubt that the atmospheric conditions were unusually 

 favourable. For when I asked the Vetturino what mountains 

 they were, he, having often passed that way without seeing 

 them, said they were nothing but clouds. I told him that I 

 knew a snow mountain when I saw it ; and as a peasant, living 

 on the spot, shortly passed, I renewed my inquiry — to which he 

 immediately answered, to my surprise, that they were the 

 mountains of Switzerland. J. HlPPISLEY 



Stoneaston, April 7 



On September 3, 1874, from the Piz Muraun, near Dissentis, 

 I saw the white dome of Mont Blanc, distant about no English 

 miles. As the Piz Muraun is only about 9500 feet I was sceptical, 

 till a reference to maps showed a line of intervening depressions. 

 I feel sure that some Alpine tourists will be able to furnish Herr 

 Metzger with cases of mountains identified at distances vastly 

 exceeding this of mine. E. Hill 



Cambridge, April 8 



The Pupil of the Eyes during Emotion 



In connection with the above subject the following experinent 

 may be of interest to your readers. It is one I made many 

 yeai 3 ago when studying the border-land between physiology and 

 psychology. At that time I showed and explained it to a number 

 of my friends. 



In this experiment it appears to the observer as if I had con- 

 trol over the muscles of the iris, as I can make the pupil of the 

 eye large or small at will. Placing myself in front of, and 

 looking towards, a window or other bright light, the observer is 

 desired to watch the pupil, and say when to contract or expand 

 it. On the order being given, the pupil is seen to expand or 

 contract as desired. This experiment can be easily made by any 

 one in the following manner : — The eye is directed towards the 

 light and a point looked at, the eye being kept steady during the 

 whole experiment. Under these conditions the bright light 

 causes the pupil to contract automatically, and when desired to 

 expand it all that is necessary is to take the attention away from 

 the eye and fix it on some other part of the body — say, by biting 

 the tongue, pinching the arm, &c. By these means the sensi- 

 tiveness of the retina is, for well-known reasons, reduced, and the 

 pupil automatically dilates. To cause it again to contract, the 

 mind has simply to be recalled to the eye and attention given to 

 the visual impressions. 



This experiment supports the explanation given by Dr. Herd- 

 man in Mr. Clark's letter in Nature, vol. xxxi. p. 433, and 

 also the explanation given by Dr. Wilks at p. 458. When the 

 mind is under the influence of fear, the energies are diverted 

 from the eyes and the pupils dilate on account of the reduced 

 sensitiveness of the retina. While in anger, sight being power- 

 fully called into action, the sensitiveness of the retina is increased 

 and the pupil automatically contracts, so that generally we might 

 expect that during those emotions in which the eyes are called 

 into action the pupils will be small, and that when the nervous 

 energies are directed away from the eyes to other centres, the 

 pupils will be large. John Aitken 



Torquay, April 8 



Notes on the Geology of the Pescadores 

 Iiuring a stay of two days in Makung Harbour in 1877, I 

 collected a few notes on the geology of this small group, which 

 has, from its recent occupation by the French, been brought 

 before the notice of the public. These islands, which were 

 briefly described in the last number of Nature (p. 540), have a 

 characteristic appearance, being flat-topped, 100 to 200 feet in 

 height, and presenting a rather barren aspect from the scarcity 

 of trees and shrubs. Dampier, who visited them in 1687, de- 

 cribed them as "much like our Dorsetshire and Wiltshire 

 Downs," producing "thick, short grass and a few trees," a 

 description equally applicable at the present day. 



A- tar as I could ascertain, the whole group was of basaltic 

 formation, the columnar structure being well developed, columns 

 30 to 40 feet high being observable in the faces of some of the 

 cliffs. In the places 1 visited the cliffs were built up of two 

 basaltic streams superimposed, the two masses towards their 

 junction being scoriaceous and amygdaloidal, and separated by 

 a layer three inches thick of a red, solt rock or laterite. The 



