L troops on one side or the other are compelled to retire, without regard to the losses which they may have suffered. and only taking account of topographical and other circumstances in a most vague and unsatisfactory manner. The second form is especially adapted to the Minor Kriegsspiel, where but a few troops are employed, and where minute records are kept of the losses of each company and fraction of a company. This produces a perfect representation of a small fight or skirmish, but involves the necessity of employing clerks or assistants, and becomes very tedious when more than two or three companies are engaged. The third form is employed when an officer of much experience can be found to take the position of umpire; one who from long familiarity with the Minor Kriegsspiel, and from practice in leading troops in action, can form a correct judgment of the possibility or results of any movement, without the necessity of making any calculations or referring to any rules. The American Kriegsspiel has gradually been developed in the United States service upon the basis of the second form above mentioned. But by the employment of several devices upon the plan itself, it dispenses with the necessity of keeping records, while it offers facilities of instantly determining the results of calculations as minute as those of the Minor Kriegsspiel. A glance at the maps during the progress of the game shows to the umpire not only the formation and position of the troops, but their present condition and previous history. Autumn manœuvres are generally recognized in the scheme of military instruction of European armies. The practice in the drillroom and on the parade-ground here find their expression and their application. They are useful in affording to officers, soldiers, and sailors an opportunity to acquire practice in their profession without the great sacrifice of life and property incidental to hostile warfare. They should therefore be made to conform as nearly to the conditions of the latter as to require a similar exercise of the faculties, and to render the forms of warfare to some extent familiar to those who have to apply them. The most perfect representation of a hostile encounter was once afforded by a distinguished soldier who thought he could save the lives of thousands of his men by occasionally sacrificing a few hun dred in the way of instruction. Who would not feel more respect for this spirit than for that of more conservative leaders who have led thousands upon thousands of brave men to be mowed down like sheep because they have vainly assumed that the methods learned by experience and hard practice would suffice to meet the requirments of modern warfare, without taking into consideration the important changes in the armament? But humanity revolts against these realistic experiments and has suggested methods that approximate as nearly to hostility as is consistent with a proper regard for human life and a measurable economy of resources; and it is by no means to be assumed that these methods are less instructive than the former. If the manœuvres are properly combined with other exercises and investigations, a system of instruction results which is even more useful than that afforded by unnecessary bloodshed, for it fixes the attention firmly upon each point in succession just as a skillful general throws all the strength of his armies upon the several fractions of his enemy and overcomes them in detail, and just as every conscientious and earnest man in other trades and professions devotes all his energies successively to mastering the difficulties of his calling. To determine how far practice in the Art of War can be taught in time of peace, and without violating what is called in the text-books the "Peace Conditions," let us consider the form of manoeuvres that differs the least from hostile encounters. In general terms, in the autumn manœuvres in Germany a condition of hostility is assumed, the forces available are divided between the opposite sides in accordance with the problem, and the exercise proceeds as if in earnest, with slight modifications to avoid unnecessary destruction of property, until the combatants come within reach of each other's weapons. The umpires then decide the effects and consequences of the firing each in his own sphere, in accordance with recognized rules and principles, based upon the experience of past warfare which has been systematized and digested for the purpose. The defeated troops then fall back as directed by the umpires, and the operations proceed until the problem has been solved, or until the time fixed for the manœuvres has expired. The following are some of the features in which this exercise differs from war: 1. The firing is not conducted with ball cartridges. 2. The troops do not fall back from fear of death. 4. The action is sometimes suspended to enable the umpires to decide the result. 5. The farmers' crops are sometimes avoided, where in war they would be trodden down. 6. The ground sometimes shelters troops from sight where they would be exposed in war. The modifications 4, 5, 6, introduced mainly with a view to economy and like considerations, are far from detracting seriously from the value of manœuvres for military instruction. On the field of battle the combatants are urged on in the heat of excitement to the attainment of certain ends, and are only too apt to be biased by their immediate surroundings, but in the manœuvres the modifications and pauses serve to fix the attention of officers and men to remoter influences. It is understood that the manœuvres of the other continental nations are similar in character to those of Germany. The method of deciding the effect of fire under all conditions is identical with that employed in Kriegsspiel, and constant practice in this exercise and applications of its principles, beginning with operations on a small scale on the map and in the field, affords to the umpires excellent preparation for their duties in the manœuvres. In making their decisions account is taken of all the modifying factors dependent upon the nature and circumstances of the troops delivering the fire and those subjected to it. It is probable in European manoeuvres these factors are not computed as in the Minor Kriegsspiel, and in the American practice, but estimated as in the freer form of this exercise. But it should be remembered that by whatever method the Kriegsspiel calculations of the effect of fire are made, they are based upon the results of the experience of war so modified as to take account of improvements in the mechanism and use of weapons, and it must not for a moment be inferred that they depend upon the results of target practice alone. Thus, military history and statistics form the basis of Kriegsspiel, as the latter forms the basis of the umpire's decisions in the manœuvres of opposing parties. The highest order of manoeuvers cannot be considered independently of Kriegsspiel, nor can the latter attain its highest usefulness unless supplemented by manoeuvers; nor can either be developed without a proper study of military history and science. MEETING 395. The History and Theory of Cohesive Construction as Applied Especially to the Timbrel Vault. BY MR. RAPHAEL GUASTAVINO. The 395th meeting of the SoCIETY OF ARTS was held at the Institute on Tuesday, November 26th, at 8 P.M., Prof. G. Lanza in the chair. After the reading of the records of the previous meeting, the chairman presented Mr. Raphael Guastavino, of New York, who continued the reading of the paper on "The History and Theory of Cohesive Construction as Applied Especially to the Timbrel Vault," which was begun at a regular meeting of the Society held October 24th. Mr. GUASTAVINO said: We will begin by investigating the way in which this kind of arch works. A "timbrel vault" of a single thickness of brick or tile has no more resistance than an arch or vault built by the "gravity system," because, no matter how good the mortar may be, there are only vertical joints, and the bricks or tiles are working as voussoirs, consequently this form of arch belongs to the gravity system, but if we put another course over the first breaking joints, and laid with hydraulic material, we will have the action of the cohesive force in this way, the mortar laid over the first course, or extrados, takes bond with it and also with the course laid on top. As soon as the cement sets, we will have shearing resistance represented by 17,820 lbs. per square foot (test No. 4873). In this manner we introduce a new additional strength to the arch. But in the gravity system the force of gravity alone is the only force keeping the voussoirs in place by pressure against each other in the joints. These joints are not protected, and any reduction in the width of the joints in consequence of pressure, or weight on the arch, compromise the setting of the mortar. For this reason, in the gravity system the mortar serves only as a cushion, also, if cement mortar, because of bad setting, and adds no strength to the arch. In our "cohesive system" with horizontal breaking joints, with 17,820 lbs. per square foot shearing strength, the reduction in the vertical joints is protected so absolutely that, 1st, we can build arches of 20 feet span only 3" thick, using a center of 1" thick, and move it along as soon as a row of tiles is laid, which usually requires about fifty minutes; 2nd, it is common to see the workmen walking over the arch, free from centers of any kind, in some hours after it is built; and 3rd, we can run the center under the arch again when it is completed, which is the most practical illustration that the arch has had the absolute repose necessary for its settlement. These three remarkable circumstances are of great value to architects, as they can be put in the specifications, and can be depended upon as absolute proof of the safety of the construction. But this horizontal breaking joint is not the only great advantage of the system, there are others, the principles of which we will try to explain. It is evident that if we were able to build an arch without joints it would be the best, having no settlement, but as the gravity system has only voussoirs of stone or brick, a certain number of joints is necessary. Let us suppose that we have a brick arch of 6 feet span; we shall have of common brick about 26 or 27 joints, these joints being of an inch thick, represent about 7 inches of mortar, which is compelled to set with all the weight of the voussoirs resting on the centers; the centers contracting, leave the weight or pressure on the mortar, preventing a good setting, and raising the center of pressure of the arch; this happens in all the brick arches, more or less. When this arch raises only 10 per cent of the full span it is very dangerous, because the development of the curve measures very little more than its cord, and the builder or contractor, knowing this, is always afraid when |