THREE:No excitementnow, I wonder
THREE:Keeping these various points in mind, an apprentice will derive both pleasure and advantage from tracing their application in steam-hammers, which may come under notice, and various modifications of the mechanism will only render investigation more interesting.
THREE:It may also be remarked that the special knowledge involved in applied mechanics is mainly to be gathered and retained by personal observation and memory, and that this part is the greater one; all the formul? relating to machine construction may be learned in a shorter time than is required to master and understand the operations which may be performed on an engine [8] lathe. Hence first lessons, learned when the mind is interested and active, should as far as possible include whatever is special; in short, no opportunity of learning special manipulation should be lost. If a wheel pattern come under notice, examine the manure in which it is framed together, the amount of draught, and how it is moulded, as well as to determine whether the teeth have true cycloidal curves.A paralysed woman who had also been flung into the street was nursed at the hospital, and lay with many others in the chapel of the Institution, which had been turned into a ward.
TWO:When the Academicians pass from the form to the matter of dogmatic philosophy, their criticisms acquire greater interest and greater weight. On this ground, their assaults are principally directed against the theology of their Stoic and Epicurean rivals. It is here in particular that151 Carneades reveals himself to us as the Hume of antiquity. Never has the case for agnosticism been more powerfully made out than by him or by the disciples whom he inspired. To the argument for the existence of supernatural beings derived from universal consent, he replies, first, that the opinion of the vulgar is worthless, and secondly, that mens beliefs about the gods are hopelessly at variance with one another, even the same divinity being made the subject of numberless discordant legends.238 He reduces the polytheistic deification of natural objects to an absurdity by forcing it back through a series of insensible gradations into absolute fetichism.239 The personification of mental qualities is similarly treated, until an hypothesis is provided for every passing mood.240 Then, turning to the more philosophical deism of the Stoics, he assails their theory of the divine benevolence with instance after instance of the apparent malevolence and iniquity to be found in Nature; vividly reminding one of the facts adduced by Mr. Herbert Spencer in confutation of the similar views held by modern English theologians.241 As against the whole theory of final causes, Carneades argues after a method which, though logically sound, could not then present itself with the authority which advancing science has more recently shown it to possess. What you Stoics, he says,152 explain as the result of conscious purpose, other philosophers, like Strato for instance, explain with equal plausibility as the result of natural causation. And such is our ignorance of the forces at work in Nature that even where no mechanical cause can be assigned, it would be presumptuous to maintain that none can exist.242 The reign of law does not necessarily prove the presence of intelligence; it is merely the evidence of a uniform movement quite consistent with all that we know about the working of unconscious forces.243 To contend, with Socrates, that the human mind must be derived from a Universal Mind pervading all Nature would logically involve the transfer of every human attribute to its original source.244 And to say that the Supreme Being, because it surpasses man, must possess an intelligence like his, is no more rational than to make the same assumption with regard to a great city because it is superior to an ant.245
TWO:The sudden and varied resistance to line shafts tends to loosen couplings, destroy gearing, and produce sudden strains that are unknown in other cases; and shafting arranged with the usual proportions for transmitting power will soon fail if applied to driving trip-hammers. Rigid connections or metal attachments ace impracticable, and a slipping belt arranged so as to have the tension varied at will is the usual and almost the only successful means of transmitting power to hammers. The motion of trip-hammers is a curious problem; a head and die weighing, together with the irons for attaching them, one hundred pounds, will, with a helve eight feet long, strike from two to three hundred blows a minute. This speed exceeds anything that could be attained by a direct reciprocal motion given to the hammer-head by a crank, and far exceeds any rate of speed that would be assumed from theoretical inference. The hammer-helve being of wood, is elastic, and acts like a vibrating spring, its vibrations keeping in unison with the speed of the tripping points. The whole machine, in fact, must be constructed upon a principle of elasticity throughout, and in this regard stands as an exception to almost every other known machine. The framing for supporting the trunnions, which one without experience would suppose should be very rigid and solid, is found to answer best when composed of timber, and still better when this timber is laid up in a manner that allows the structure to spring and [107] yield. Starting at the dies, and following back through the details of a trip-hammer to the driving power, the apprentice may note how many parts contribute to this principle of elasticity: Firstthe wooden helve, both in front of and behind the trunnion; nextthe trunnion bar, which is usually a flat section mounted on pivot points; thirdthe elasticity of the framing called the 'husk,' and finally the frictional belt. This will convey an idea of the elasticity required in connecting the hammer-head with the driving power, a matter to be borne in mind, as it will be again referred to.