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470 had previously been both of woman suffrage and indeed of all aspects of the higher education of women. He died at Oxford, Sept. 25 1920.

His elder brother, (1834–1919), also a classical scholar and fellow of Merton College, Oxford, died at Rugby, Oct. 18 1919.

SIDGWICK, ELEANOR MILDRED (1845–), British educationalist, was born in Scotland, March 11 1845, the daughter of James Balfour of Whittingehame and his wife Lady Blanche Cecil. She was thus the sister of Mr. Arthur James Balfour. She was educated at home, and in 1876 married the philosopher Henry Sidgwick (see ). Mr. and Mrs. Sidgwick were both much interested in the advancement of the higher education of women, and were actively concerned in the founding (1880) of Newnham College, Cambridge, of which Miss Clough was the first principal. On the death of Miss Clough in 1892, Mrs. Sidgwick succeeded her as principal, and retained the position until 1910. In that year she retired, and until 1919 was bursar of the college. Mrs. Sidgwick shared her husband's interest in psychical phenomena, and in 1910 became secretary of the Society for Psychical Research.

SIEGECRAFT AND SIEGE WARFARE.—The earlier article on  reviews the prevailing ideas of defence against siege-warfare just before the World War. Opinion was then still unsettled on fundamental points, as well as on those differences in arrangement of the available elements of defence which have always divided the military engineering world into two or more schools. In the earlier days, Vauban and his competitors might disagree as to design, but they were in agreement as to purpose; and even at a later date, when the "bastion" school carried on its controversies with the "polygonal" or caponnière school, there was complete unity as to the necessity of permanent fortifications and substantial unity as to their functions. But the economic history of the 19th century, and the military history of its latter half, had brought the principles as well as the practice of fortification into the melting-pot.

Amongst many reasons for this, the following were the more important:—

(a) The increased size of armies, made possible by the credit system of finance, the universal service system of recruiting, the industrial system which could arm them, and the road and rail system which enabled them to disperse without risk in order to feed on the countryside, or to remain massed without starving through a breakdown of convoys, or both.

This increased size soon reached a point at which the old- fashioned fortress ceased to be an adequate base for the army's depots, or an adequate shelter in which to refit after defeat. There were signs of this even in 1870, although by that date the fortress had expanded into an entrenched camp of large perimeter, and between 1870 and 1914 the scale of field artillery, field trans- port and field ammunition for a given force, was practically doubled.

(b) The character of war, as between " armed nations," in which, in principle, a speedy decision by battle was sought at all costs, whereas warfare between the old professional armies had been prolonged from campaign to campaign. The objects sought by each side were now rather spiritual than material, or at any rate more general than local; and the fortress, which used to be judged according to the degree of protection it gave to the material objects of enemy desire a city, a province, a port came to be judged according to the degree in which it aided or impeded the manoeuvres of a field army seeking to win the war in battle. The task of fortification thus became much less posi- tive and definite, and a programme of works took on a some- what speculative character.

(c) Development of communications, which, besides the effects referred to under (a), had that of making civilized countries everywhere or nearly everywhere penetrable. The fortress as conceived of in the i8th and early igth century, therefore, no longer exercised any power of control beyond the range of its guns or the striking radius of its semi-mobile garrison. And it could easily be " turned," and then either enveloped or by

means of a masking force eliminated as a factor in the campai Cases indeed remained, and still remain, of " obligatory points of passage," where local control of the route by means of fortifi- cation implies strategic control of the adjacent regions which are limited for their intercommunication to that route. Especially is this true still of rail communication. But in the main, armies and their transport can, in present-day west and central Europe, move where they will, except through areas directly under the tactical control of fortifications.

Further, the rapidity of communication as well as the wealth of routes enables a modern state to concentrate its defensive forces in the threatened region far more rapidly than of old, and the necessity for fixed defences, to gain time for the assembly of mobile forces, steadily declined.

(d) The development of the technique and manufacture of weapons of war, from about 1860, became so rapid that permanent fortifications of any given design were liable, like modern war- ships, to fall into obsolescence after a brief life of usefulness which contrasted sadly with the long career of a place like the old citadel of Antwerp, built in 1567 and besieged with all the forms and means of siegecraft in 1832.

Three out of four of these operating causes, it will be noted, are extrinsic, and one only intrinsic. In the case of the latter, operating alone, it is easy to conceive of a sort of duel between the gun constructor and the military engineer, analogous to the con- tinued contest of gun versus armour plate. Few fortresses have ever had the good fortune to be fully up to date in design and equipment at the moment of siege. The reply of the French engineer who was asked what he would do if the Germans made the length of their scaling ladders greater than the depth of his ditches, expresses an inevitable condition of permanent fortifica- tion design. " It will always be easier," he said, " for the Ger- mans to make scaling ladders than for me to dig ditches." Simi- larly, it will always be easier to make a new gun that will cut through a given thickness of concrete or armour than to increase the latter. For questions of expense apart the fort is a per- manent sentry guarding against surprise, and the reconstruction of its works is a heavy piece of engineering which not only takes time but frequently renders them useless for the period of the repairs. Thus, in 1914, war surprised the fortress of Belfort when four of its principal works were under reconstruction. And if, as is generally the case, the programme of recon- struction is so drawn up as to minimize these risks, some part of the fortification system is sure to be obsolescent at any given moment. At any such moment, then, the question is not whether the means of attack have the upper hand practically this is almost always the case but whether the superiority is of such an order that the fortress or fort is useless. The new long-ranging powers of siege artillery in 1870, subjecting the area intra muros to concentric bombardment by an indefinitely numerous attack- ing artillery, and the demolishing powers of the superheavy siege howitzers evolved in Germany and Austria between 1900 and 1914 at least as against average concrete were superiorities of that order. But such cases are not frequent in military history, and it is more usual in modern times, especially to find a sort of thrust and parry, in which the artillery of the attack maintains a lead, but not a decisive lead.

The extrinsic causes in operation, meantime, were tending to bring about radical changes in the very meaning of fortification.

Outwardly, the controversies of the period 1885-1914 turned on technical questions, and chiefly on whether improvised fortifications could be shown to possess a resisting value practically equivalent to that of permanent fortifications. But in reality it was the feeling that the purposes and principles of fortification,