At the same time an individual who himself shows no indication of any parental peculiarity may yet pass it on to his offspring, constituting what is described as patency and latency, as is seen in homophilia and certain other diseases. It seems likely that what is commonly known as prepotency, dominance, and patency and latency, may be embraced within the laws which were first discovered by Gregor Mendel, Abbot of Brünn, fifty years ago, and which are now known as Mendel's Laws. Mendel's conclusions, drawn from experiments on peas, were long unknown to the world; but their rediscovery has given an enormous impetus to similar enquiries, and during the last few years numerous investigations have been made with the object of ascertaining whether his results are applicable to man. regard to some qualities this has been shown to be the and it now seems to be established that such abnormalities as brachydactyly, colour-blindness, night-blindness and congenital cataract are transmitted in accordance with Mendelian laws. Is this so with the neuropathic diathesis, which we may certainly consider the most important form of degeneracy from the sociological aspect?

case;

With

Researches which have been made under the auspices of the Eugenics Record Office of America proclaim that this is the case, and that 'the fact of the hereditary transmission of the neuropathic constitution as a recessive trait, in accordance with the Mendelian theory, may be regarded as definitely established.' But the difficulties and sources of possible fallacy attendant upon such enquiries are so great that one must accept these conclusions with considerable reserve. It is impossible to deal adequately with the question in this place, but it may be remarked that a person may be of neuropathic constitution and yet pass through life apparently normal, owing to the absence of any direct excitant to a mental breakdown; in other words, he may inherit a predisposition to insanity and yet, in consequence of his life being cast amid healthy surroundings devoid of strain, never become insane. The ascertainment of the number of offspring who are hereditarily affected thus becomes a matter of the greatest difficulty, and yet this is essential in order to prove that the transmission is in accordance

with Mendelism. My own experience is that, while all the offspring of two markedly degenerate persons are always defective, the children resulting from the union of a pronounced degenerate with a healthy individual tend to be, not some normal and some abnormal, but all of them of abnormal constitution. If one parent only bears the taint in slight degree, it is not uncommon to find some children affected while others entirely escape; but even here it is by no means rare for all the children to evince a distinct psychopathic failing. Whilst, therefore, it is hazardous to dogmatise on the subject-for the facts are by no means conclusive-the available evidence seems to suggest that the inheritance is more often of the blended than of the Mendelian type.

I have spoken of the pronounced grades of mental defect as being the culmination of degeneracy; but it is not always thus cumulative, and it is possible that the mating of a person suffering from a milder degree of germinal impairment with healthy stock might, after a few generations, lead to the eradication of the impairment and so to regeneracy. But the experiment would be somewhat hazardous for the individual offspring. Severe exciting factors might readily fan the slumbering spark into a violent flame; and this is probably the explanation of many so-called sporadic cases of insanity and even of mental deficiency. Such exciting factors may be supplied by injury during birth, infectious disease during childhood, excess or strain during adolescence or maturity, or indeed any untoward condition of the environment, whether of intra- or extra-uterine life. And, should the germinal impairment be still more pronounced, it seems highly probable not only that mating with healthy stock is powerless to neutralise the defect, but that there is the greatest danger of a considerable reduction of the mental vigour and durability of all the offspring and consequently of a marked decline in the net capacity of the community. It is by such means that I conceive that a nation, while still surviving, may not only lose its power to advance, but may be rendered incapable of successful competition against its more vigorous neighbours and so sink to a lower plane. And when we take into account the neutralisation of the force of natural selection which occurs in a civilised as Vol. 228.-No. 452.

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opposed to a more barbarous community, and which prevents the elimination of these unsound members, it is not difficult to understand how it has come about that nations which have reached a high degree of civilisation should in course of time have been overrun by a horde of barbarians. For with nations, as with individuals, it

is the 'fit' who survive.

It may safely be said that the problem of degeneracy has now passed beyond the academic stage, and that its practical importance is recognised by most thoughtful persons. But its pressing nature is still unrealised; and it is, perhaps, not unnatural that, in the midst of the greatest war the world has ever known, it should be regarded as a question which can well await the return of peace. There could be no greater mistake. The military necessities of the country and the large number of casualties have already emphasised the importance of 'man-power' and directed attention towards the declining birth-rate and the conservation of child life. All this is quite right and proper; but it is an incontrovertible fact that the many medical rejections and the system of voluntary service have both led to these casualties being disproportionately incident upon the most fit, and that the general effect of the war has been to augment still further the previously existing tendency towards the survival of the least fit. And there is great danger that an indiscriminate increase in the birth-rate, a demand for quantity irrespective of quality, may still further contribute towards this result. Let us make no mistake. The ending of the war will not end international competition; and, if we are to maintain our national or economic supremacy, we shall need, not merely men and women, but the best men and women we can produce. If we are to do this, the problem of degeneracy must have a place in any scheme for increasing the birth-rate and building up the future manpower of the Nation.

A. F. TREDGOLD.

Art. 3. THE SOUND OF A GREAT EXPLOSION.

ON Jan. 19, at 6.51 p.m., a great explosion-perhaps the greatest ever experienced in these islands-occurred at an important munitions factory in East London. The factory in question is well known, and it will therefore be sufficient if its position be represented roughly by the star in the accompanying map.

The interest of the explosion from a scientific point of view is indirect and lies in the evidence which it offers on the mode in which sound travels through the atmosphere. In this explosion, as in so many others, the area over which the sound was heard is not continuous; it consists of two detached portions. One portion, of course, surrounds East London. It will be convenient to call it the 'inner sound-area.' The other lies far away to the north, and may be known as the 'outer soundarea.' Between the two, there lies a broad 'zone of silence,' in which, with one exception, all trace of the sound seems to have been lost. There is nothing novel in this fact. It has been well known since the beginning of the century, when the minute-guns fired during Queen Victoria's funeral procession revealed the existence of a silent zone for the first time. Many subsequent explosions, both artificial and natural, have exhibited a similar zone. The peculiarity of the recent explosion is that it occurred in, and manifested its effects over, a populous district, from which a large number of observations could be easily obtained.

The continuous lines in the accompanying map bound the two areas over which the sound was heard. They depend on an unusually large number of observations (571 from 391 places). It was essential, however, to show that the intermediate district was really free from all trace of sound, and I therefore made inquiries at many places within the silent zone and especially at those close to the boundaries as I had drawn them. Similar letters were also sent to places just outside both sound-areas. The position of these places (71 in number) aided materially in the exact delineation of the boundaries.

Cf. the article on 'The sound of big guns' in the Q. R. for July 1916.

The inner sound-area, as will be seen from this map, is of rather unusual form. It shows a marked extension in two directions, one towards the east-south-east, terminating near Canterbury at a distance of 48 miles from the source of sound; the other running in a northwesterly direction through Hertfordshire and Bedfordshire, and ending just beyond Northampton after a course of not less than 66 miles. In comparison with its distortion along these two lines, the restriction of the sound-area in other directions is all the more remarkable. Towards the north-east and south, the boundary passes through points which are only 20 and 19 miles respectively from the origin. The total area included within the inner boundary curve is 3390 square miles.

Of very different form is the outer sound-area. It stretches in a broad band, in a direction a little south of east, from the neighbourhood of Nottingham to, and no doubt slightly beyond, the east coast of Norfolk. Its length, as far as the coast-line, is 131 miles, its greatest width is 44 miles, and the area covered by it is 5000 square miles, or half as large again as the other. Near its northern boundary lie the most distant places at which the sound was certainly heard-Bestwood (near Nottingham) and Stow (near Lincoln), which are respectively 117 and 128 miles from the origin.

For a great explosion, these distances are by no means excessive. Possibly, the amount of explosives lost was not so considerable as in other explosions; but on this point we cannot expect to be enlightened. At any rate, the distances are smaller than that attained by the soundwaves of the Wiener-Neustadt explosion on June 7, 1912, when 197 tons of gunpowder exploded and the sound was heard to a maximum distance of 186 miles.

The observations which I have received from the two sound-areas point to great variations in the loudness of the sound. The epithets used show that the sound may be readily divided into three grades of intensity. In the highest (A), the sound was evidently very loud. Such terms are used as a terrible explosion,' or 'louder than any bomb or crash of thunder.' In the next (B), the sound was moderately loud, as is clear from such expressions as a loud report,' 'heavy gun fire' or 'a heavy clap of thunder.' To the lowest grade (C), that of faint

'a