171 



AISLE. 



ALARUM. 



in 



below the larger, and separated from it by a plate forming tho bottom 

 of the upper and the top of the lower cylinder. A piston-rod, common 

 to both cylinders, pu*(* through a stuffing-box in the plate, attached 

 to which are two valved plotting, working in their respective cylinders. 

 The advantage of thin construction is, that the pressure of the external 

 air on the oiled silk valve of the larger cylinder in taken off by the 

 vacuum formed in the smaller one, and in consequence no greater 

 resistance is offered by the valve than that arising from it* adhesion 

 and tension. The exhaustion of this pump is very rapid, and in the 

 trial amounted to 0"24 inch of mercury." The motion of the pistons is 

 fleotd by means of a short crank with a jointed connecting-rod, con- 

 verting the circular motion given by the lever handle into a vertic.il 

 one, which in maintained by means of a cross-head with rollers working 

 between guides. Thin pump is more particularly described in Mr. 

 Ti>iulinxi>n'x Rudimentary Treatise on Pneumatics.' 



In the air-pump exhibited by Varley and Sous a new construction is 

 adopted. "It is worked by a continuous rotatory motion of the 

 handle, slide-valves being used to open and close the communication. 

 On the piston arriving at one end to expel air from the barrel, it is 

 followed by rarefied air from the receiver ; the slide-valve closes upon 

 the receiver and connects the two sides of the piston ; the residual air 

 expands into the larger space, becomes equally rarefied, and the subse- 

 quent motion of the valve separates these spaces, and connects the 

 receiver with the closed end. The piston then returns to exhaust air 

 into thk end of the barrel and to expel it from the other, and thus 

 continuous exhaustion is kept up ; for, how rare soever the air be- 

 comes, it keeps flowing after the piston continually. The barrel is 

 twice filled for every entire revolution of the handle. This pump 

 hat a single barrel with double action ; it exhaust* quickly, and the 

 exhaustion was found to be 0-05 inch for a moment, but could not be 

 maintained." 



In the French department, the double-barrelled air-pump exhibited 

 by M. Breton had, instead of valves, a glass plate sliding over apertures 

 communicating with the receiver, and the pumps and the motion of 

 this glass plate is produced by the mechanism which works the pump. 

 " The approximate exhaustion is first made by the ordinary alternate 

 action of the barrels. The system of communication is then changed 

 by shifting round the glass plate, which serves as a valve during one- 

 fourth of a revolution, when the rarefied air is condensed in one barrel 

 and sucked into the other, whence it is ultimately ejected through a valve 

 of oiled silk very close to the piston." In the air-pump exhibited by 

 M. Deleuil, the barrels were of glass, and the valves, after M. Babinet'g 

 plan, were opened by means of wires passing through the pistons. The 

 opening of the valves i thus rendered independent of the elastic force 

 of the air left in the receiver, and the degree of exhaustion must depend 

 on the air remaining after the action of the piston. 



AISLE, or AILE (in Architecture), indirectly from the Latin word 

 /, a wing, through the French tale, which has the same signification. 

 In French, this term is applied to the outlying and returning ends of a 

 building, which we distinguish by its English equivalent, mmj; such are 

 the columned ends of the front of the British Museum. We apply the 

 term aisle to the lateral divisions or passages of the interior of a church 

 those parts which lie between the flank walls and the piers, pillars, 

 or columns, which flank the nave, or grand central division when the 

 structure is so arranged. Sometimes, but incorrectly, with reference 

 to modern churches and chapels in this country, the mere passages or 

 corridors which run between, and give access to the pews, are called 

 aisles. Still more incorrectly, some writers, and even ecclesiastical 

 writers, have called all the longitudinal divisions of the body of a 

 church, aisles, thus including the nave under a designation which 

 In-long* only to its adjuncts anil accessories. 



The division of a rliurcli into what we term nave and aisles an we 

 imply out of the difficulty which existed of H|mnning a great breadth 

 with a roof without ome intermediate support ; and thus the greater 

 Constant in ian churches or lianilicax of Rome were built with four rows 

 of column-, forming five longitudinal divisions ; that is, with two aisles 

 on each side of the nave. This was imitated in subsequent structures, 

 and the nictn>|>olitan churches of Milan and Paris were built in five 

 divisions, or with four aisles, ox they exist at the present time. That 

 the custom of arranging the interiors of churches with aisles was con- 

 tinued in deference to ecclesiastical precedent, or at any rate long after 

 the uecunty for using the props which form them ceased architectu- 

 rally, may be rendered dear by reference to the following fact. Most 

 of our cathedrals and greater churches in this country ore of later 

 date than the roof of Westminster Hall, which, without intermediate 

 support, spans a greater breadth tlian most of them can boast of; 

 and yet they are, as a general rule, all divided into nave and aisles. 

 In recent Ciotliic churches it is needless to add they arc rontinm-d, 

 eren when, as in some of very small size, they are at once obstructive 

 and costly. 



In some Engluh books, though |>iha|w in none of th>> present 

 century, this term will be found written without the a Me. 



ALANINE (C,H,NO,V When aldehyd-ammonia is acted on by 

 hydrocyanic acid, and an excen of hydrochloric acid, a crystalline body, 

 soluble in water, is formed, to which Ntrecker has given the name 

 alanine. It crystallise* in groups of prisms, which are insoluble in 

 ether, nearly go in alcohol. It solution has no effect upon test-papers. 

 It sublime* at about 400*. It is homologous with glyncoll and l<ti>in>. 



and isomeric with hrlamidt, tirttliar, and MironV. When acted on 

 by hypouitrous acid it is converted into lactic acid, as follows : 



U .:,.:... 



3.C..H,.0. 

 Lactic Acid. 



ALARUM. It is curious to mark how much ingenuity linn been 

 displayed within the last few years in the invention of aimim*. and 

 how many patents have been taken out for the inventions. In i, 

 these contrivances there is some little bit of mechanism which gives a 

 shrill sound whenever attention is required to be directed to an 

 jr. -i with which the alarum is associated. 



Without describing any of the older forms, we may glance at a few 

 of the modern suggestions. The ' travellers' alarum ' is a small bran box 

 about 24 inches in diameter by 1 J thick. It has hands which may 

 be set to any hour to awaken a sleeper. Mr. Allen, in 1844, registered 

 an alarum intended to prevent injury to boilers from the water falling 

 below its proper level; it consists of a float within the boiler, a 

 steam-whistle on the exterior, and a tube of connection: \\hen the 

 water is at a proper height ill the boiler, the float i ip, and 



the whistle is silent; but when the water, and with it the float, 

 descend too low, a little valve in the tube opens, and a current of steam 

 from the boiler ascends to the whistle, which immediately gives forth 

 a shrill sound, thereby indicating that the water has sunk too low in 

 the boiler. 



An alarum patented by Mr. Doull, is a ' railway whistle,' so con- 

 structed as to yield several notes, capable of being combined into a code 

 of signals. A ' chemical alarum ' by Mr. Mowbray consists of a copper 

 cylinder, with a whistle at the top ; a piece of carbonate of HUM and 

 a little muriatic acid are put into the cylinder, by which carbonic acid 

 gas is speedily generated ; and this is forced by some kind of mechanism 

 into the whistle, whenever a sound is required to IK- produced. A 

 contrivance by Mr. Hoare, described before the Society of Arl 

 gists of a chain of rods extending from end to end of a railway train, 

 and moving freely on joints ; at the end of the chain, in the guard's 

 carriage, is a crank which, when the rods rotate on their axes, comes 

 in contact with a hammer, and causes it to strike a bell ; the driver, 

 or the passengers in any carriage, can give a slight rotatory motion to 

 the rods, and thus signals may be communicated. Up to the present 

 time, however, all kinds of railway train signals have been sadly 

 neglected. See further on this subject under RAILWAY. 



But the busiest contriver of alarums, perhaps, is Mr. Rutter, who has 

 called to his aid the man-els of electricity. In a patent tot 

 contrivances, taken out by him in 1847, one variety is tin- Fire Alarm', 

 a complicated apparatus intended for use in large buildings. A galvanic 

 battery is placed in one room, the alarum in another, then 

 every room, and copper wires to connect all these pieces of app. 

 If the temperature of any room be greatly raised, as by accidental fire 

 the rising mercury in the thermometer comes in contact with a metallic 

 wire, which set the galvanic battery in action, and this again works 

 the alarum-bell in the same way as an electro-telegraphic clock, but 

 with an adjustment intended to show in which room the rise of tempe- 

 rature has occurred. A second variety, the ' Trespass Alarum,' dt'i>cnds 

 for its action on the placing, near every door and window, of a tube 

 containing mercury, open at the top ; the opening or closing of the 

 door or window brings a small wire into contact with the surface 

 mercury, and this completes a galvanic connection with a battery in 

 another room : all the parts of the apjaiatus may lie the same as those 

 in the fire alarum, except by having open tubes of iii<-uui\ m-ardoon 

 and windows, instead of thermometers in each room. A third variety, 

 the ' Railway Alarum,' in intended to establish signals of communica- 

 tion between the guard and the engine-driver of a railway tiam. 

 There is a copper wire carried through or U|HUI or l>eneath each 

 carriage, and connected with another in the adjoining carriage by a 

 flexible metallic cord : the wire and cord being coated with gutt.i 

 lTrlm to secure isolation. There is thus a wire communication from 

 end to end of the train. The guard has in his box or seat, a very sm.ill 

 galvanic IwUcry : and the engine-driver has a Reries of small studs 

 connected with tho rail on which his band is usually resting. \\ I,, n 

 the guard wishes to communicate with the engine-driver, he sends a 

 slight galvanic shock through the wire to the spot on which the hand 

 of the driver rests ; and the duplication or variation of the shock may 

 lw mode to indicate various signals. It must be. evident that great 

 completeness and exactness would be necessary to rcndi-r any of the 

 above three kinds of alarum efficient for the purputtc intended ; and it 

 may be added that, as yet, the contrivance* have not com.- into 

 actual use. 



A tloating alarum wan suggested a few years ago by Mr Hobbs, of 

 Bristol, to be moored to a sunken rock or other dangerous place at sea, 

 Tin- centre of tin- maehinr is an air-vessel or buoy. At each end is a 

 box in which a whistle is fixed, whose mouth is protected from tin- 

 water. As the water of the sea circulates in certain jnrt# of the interior 

 of the machine, it drives the air alternately from one end to the other, 

 and impels it through the whistles; and the more violently the 

 sea rocks tho floating machine, the louder will the whistles give 

 forth their sound. The proposal of the inventor is to make the buoy 

 and whistles of such dimensions that the sound may be heard some 

 miles distant. [BuoTg.] 



