46 



NA TURE 



\_Nov. 



In one respect the observations are incomplete, and need to 

 be supplemented at some future time. Within the lighthouse the 

 source of light is surrounded by an apparatus which gathers 

 together the light sent forth in all directions, excepting a small 

 angle above and below. Thus, the intensity of the light sent in 

 a sloping direction upwards and downwards is of as great im- 

 portance as that of the light sent forth in the horizontal plane. 

 But only the latter has hitherto been measured in the photo- 

 metric gallery. According to M. AUard the electric arc pro- 

 duced by an alternate current sends out horizontally an amount 

 of light which is ii percent, greater than the average amount 

 sent in all directions. With a continuous current the strongest 

 light is thrown on the side opposite to the positive carbon ; but 

 it happens that with an arc light of this description horizontal 

 measurement gives the average value. Probably Mr. Wigham's 

 wide cluster of g.as jets sends forth less light horizontally, owing 

 to the imperfect transparency of one flame to the light of another, 

 than it sends in an upward direction ; and the same may be the 

 case with the concentric gas-burners and oil lamps. Minors 

 might hereafter be arranged within the photometric gallery, which 

 would serve for making these measurements. 



To determine accurately at a distance the power of the various 

 lights exhibited was an essential preliminary to calculating the 

 range of any of the lights in hazy weather. And although this 

 power is appro.ximately calculable, the power and dimensions 

 of each flame, and the structui-e of each lens being known, it was 

 of great interest to make actual measurements of the intensity of 

 the light at two different points, and in different states of the 

 atmosphere. I am not aware that such measurements had ever 

 before been attempted. Owing to the novelty of the photo- 

 metric problem, .and to some extent of the methods employed, it 

 was highly important to have some means of testing how far the 

 results were trustworthy. Such means were furnished by the 

 multiform system of Mr. Wigham. At any distance, and in any 

 state of the atmosphere, the illumination produced by a com- 

 bination of two or more similar lamps and lenses is so many times 

 as great as the illumination produced by a single lamp and lens 

 of the same kind. Thus, among the lights to be measured were 

 several whose relative power was known beforehand. If testings 

 of single and multiform lights, made in succession while the 

 degree of clearness of the air was unchanged, gave values vary- 

 ing approximately as the number of lights, an equal dsgree 

 of exactness may be ascribed to the testings of other lights and 

 lenses. 



On July 12, the weather being "clear, calm, overcast," the 

 light from the single, biform, triform, and quadriform io8-jet 

 burners, showing through Mew Island lenses, was measured at 

 hut I. The results in thousands of candles were 50, 98, 16S, 

 and 214. Three testings intervened between the second and 

 third, and probably the air had become a little clearer, but the 

 numbers are not far from the ratio i, 2, 3, 4. Three days later 

 the same single, triform, and quadriform combinations were 

 tested one after the other, also at hut I. The values found 

 are 48, 145, and 186. .Similar testings were made on July 23, 

 on a clearer night, of all four combinations ; their power was 

 found to be 58, 112, 171, and 220 thousands of candles. Pro- 

 bable values in the ratio of i, 2, 3, 4, are 56, 112, 168, and 

 224. On the same night the value found for a single six-wick 

 oil lamp behind .an Eddystone lens was 56,000 candles, and for 

 three such lamps behind three such lenses 168,000 candles. On 

 November I, in thick haze, the value found at the nearer hut 

 for " I. Gas, 108, M.," was 25,500 candles, and for " IV. Gas, 

 108, M.," 102,000. The results obtained at hut II., with a 

 wholly different photometer, are confirmed in tlie same manner. 

 For example, on February 7, consecutive testings on a misty 

 night of "single" and "quadriform gas" gave in thousands of 

 candles the numbers 26 and loi. On March 20, on a very 

 clear night, the values found for the same two lights were 63 

 and 252. 



In looking over the tables of the photometric record, and 

 comparing the figures standing against combinations of equal 

 numbers of oil lamps behind Eddystone lenses, and of the larger 

 gas-burners behind Mew Island lenses, in all weathers in which 

 the lights were measurable, the eye is struck by the similarity of 

 the numbers. The rival systems are nearly equal ; there is little 

 to choose between them. Still less difference, as has been 

 pointed out, was discernible on looking, as we did night after 

 night, at the lights themselves. Other considerations than that 

 of visibility in either clear or hazy whether, must decide whichi 



if either, of the two systems is to be generally adopted for light- 

 ing our coasts. By multiplying burners and lenses, and by 

 enlarging the size of the lenses, more powerful lights still 

 may Ije produced, if it is thought desirable, with either 

 illuminant. 



But the most prominent fact on the face of the photometric 

 record is the immense superiority of the electric light. The 

 conclusion forces itself upon the reader of these tables that if 

 greater power is needed, it is to be found, not by magnifying 

 lenses or multiplying combinations of gas or oil burners, but by 

 substituting the light of the electric arc. 



The Trinity House Committee report that the electric light in 

 clear weather is certainly not popular with sailors, chiefly on 

 account of its dazzling effect at short ranges. But at ranges 

 exceeding two or three miles, "hyper-radiant," or even multi- 

 form lenses, are not visibly larger than such a lens as is suitable 

 to the electric arc ; and at such ranges the " dazzling effect " is 

 simply that due to the power of the light. If a double quadri- 

 form were as powerful it would dazzle as much. Also the use of 

 a powerful electric arc in clear weather may be avoided. It 

 would not be difficult to arrange for the use of a small electric 

 arc during clear weather, and the quick substitution of a power- 

 ful arc light when the weather became hazy. I would venture 

 to suggest that the singular circumstance which led or contributed 

 to the removal of the electric light at Dungeness, that a vessel 

 went ashore near the lighthouse, may have been due, not to the 

 dazzling effect of the light, but rather to the diminution of bright- 

 ness as the approaching vessel passed within and beneath the 

 range of the light. With the condensed and sharply-defined 

 beam of the electric light, it may perhaps be desirable to devote 

 some part of the optical apparatus to spreading a portion of the 

 light over the space intervening between the co.ast and the point, 

 a mile or two away, at which the principal beam first strikes the 

 sea. If this is done, the light at short ranges might be made 

 sufficient, but not too dazzling ; and for longer ranges there seems 

 to be no reason why the powerful beam produced by the electric 

 arc behind one of the Mew Island lenses should not be em- 

 ployed. This beam bad a divergence of about 1°. Even from 

 the high level of the South Foreland lights, if the axis of such a 

 beam were so inclined that only about \ of the light p.assed 

 over the horizon, the full light would extend to within about 

 three miles of the shore. Since the apparent brightness of 

 every light must vaiy with the state of the atmosphere, as well 

 as with the distance of the light, and as the angle subtended, 

 even by a multiform light, at a few miles distance is very small, 

 it cannot be possible by the appearance of a light without other 

 data to judge of its distance. The electric light is not singular 

 in this respect. 



( To be continued. ) 



THE LUMBAR CURVE IN MAN AND APES 



V^E are indebted to Prof. Cunningham, of Trinity College, 

 '' Dublin, for a well-illustrated and exhaustive memoir on 

 the subject of the lumbar curve in man and apes. This memoir 

 has been printed by the Royal Irish Academy as one of the 

 Cunningham Memoirs, and is illustrated by thirteen plates, 

 seVeral of which are large folding ones, and two of which are 

 large coloured drawings of the two surfaces of a mesial section 

 of a male chimpanzee ; these are life-size, and are the first 

 accurate representations of the topographical anatomy of this 

 anthropomorphic ape we have seen. 



The structural differences between man and the anthropoid 

 apes are no doubt in a great measure due to the assumption by 

 man of an erect attitude, and to his having from an early period 

 of his life dispensed with the use of his anterior extremities as 

 organs of locomotion. The vertebral column of man might be 

 expected to exhibit in a marked degree differences distinguishing 

 it from other animals, and that more or less deep convexity 

 forwards in the region of the loins has been considered by some 

 not only as a marked character of the human spine but even as 

 peculiar to humjinity ; other anatomists have denied that this is 

 so, and consider that man and certain of the man-like apes have 

 it in common. In this memoir Prof. Cunningham seems to 

 minimise the importance of the lumbar curve as a distinctive 

 character of any special group. Not only the higher, but also 

 the majority of the lower apes, possess this curve ; and, under 



