1841.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



183 



action. Certainly not from the overplus action, but undoubteiUy from 

 the deflecting magnetic action, for it is evidently just a case of the 

 third law of motion ; that action and reaction are equal and contrary : 

 a very satisfactory explanation, yet what an effort is made to obscure 

 the subject!* 



The writer now drives the apparatus with a winch, and supposes 

 the magnetic attraction to perform the business of cohesion, and then 

 asks if his hand imparts the centrifugal force. This requires no 

 answer from me, and he has thought fit not to do so either. 



His illustration in the case of a sling, I confess I luiderstand not. It 

 involves the absurdity of expressing velocity in terms of weight; al- 

 though, as I understand it, it ought to be told in terms of space and 

 time. 



The instance of the fly-wheel has little new, except the manifesta- 

 tion of another misconception of the writer's. " The central (centri- 

 fugal) force, says he, acts by pressure, and a resultant from that pres- 

 sure and tlie force in the circle is the consequence, but so long as 

 resistance from cohesion continues, neither motion nor pressure can, 

 be imparted to another body by the central force." The writer here 

 exchanges cause and effect, for he would fain attribute a self-exciting 

 property to the centrifugal force, and insinuates accordingly that the 

 resistance of cohesion is the covuqiiaii centripetal force. Whereas 

 the reverse is the case; the cohesion is exerted, because it perpetually 

 winds the direction of projectile motion; and the centrifugal force is 

 plainly the inertktic (forgive the innovation) tendency of the body to 

 rectilinear motion. There is also something said of moment of rota- 

 tion, irrelevant to the subject. 



The experiment of the whirling table simply confirms what was 



proved long ago, that, using the writer's symbols, .r =^ — . 



After recapitulation, he concludes the first part of the subject with 

 the notable inference, that centrifugal force is a physical agent, excited 

 by an inscrutable law of nature when matter moves curvilinearly. I 

 need not say how unnecessarily this law has been brought forward. It 

 really would be more surprising than the formation of magnets by 

 electric operations. For electricity and magnetism are identical, and 

 therefore naturally enough such a result should take place. Though 

 we may not know the absolute nature of physical principles, we may 

 accurately know their relative nature. Therefore the writer is un- 

 fortunate in his allusion, as we are dealing in relatives, not in absolutes. 



Proceed we to the second part of the subject: the composition of 

 the projectile and centrifugal forces. And here an absurdity at once 

 presents itself. We are told that a ball weighing 1 !tj. moving in a 

 circle of 2 feet radius, at the rate of two revolutions per second, has a 

 projectile velocity of ■25-14 per second, and a centrifugal velocity of 

 157"76 per second. This number has evidently been the result of the 



formula — , which expresses the proposition quoted from Brewster's 



25-14= 

 Encyclopedia. For — - — =: 1 57-76 feet. Now, it is a misnomer to 



call this the velocity per second. It is the space passed through in a 

 second by the body, with a motion accelerated from nothing. We 



might as well say that 



157-7G 



: 78'SS feet would be the space passed 



through per half second. But what would the rule give us ? The 

 projectile velocity per half second being 12-57, we woidd have by 



V- 12-572 

 the rule ^ =; — - — = 39-44 feet per half second : ludicrously incon- 

 sistent. The writer places the two forces on the same footing, whereas 

 the one is impulse, the other pressure; which renders tlie succeeding 

 reasoning a baseless fabric. I have shown at the commencement of 

 this paper, which I fear is too long, that the shorter the time supposed 

 for action, the less is the ratio of the effects of the projectile and cen- 

 tripetal forces, and therefore in any moment of time, the effect of the 

 latter is unassignably less than that of the former. If he will turn also 

 to Cavallo, whom he has so often quoted, he will find the same con- 

 clusion come to in his third proposition on curvilinear motion. 



The experiment with the tube and balls, though it has the appear- 

 ance of accuracy, is undoubtedly pointless. The apparatus must have 

 been exceedingly clumsy to require "very high increasing velocities" 

 to manifest the action of this wonderful power. 



' The idea of the perpendicularity of Iheir dircclions preventing their 

 annual action is very absurd. What is parabolic motion ? 



"As to the probable results of a practical application of this princi- 

 ple," they will be exactly nothing at all, as the experiment with the 

 tube and balls well nigh proves. 



I am, Sir, your obedient servant, 



Daniel Clark. 

 Phcenix Iron JVurks, 

 Glasgow, May 10, 1S41. 



ON THE EMPLOYMENT OF MILITARY ENGINEERS. 



Sir — In your last month's Journal, under the above head, I find an 

 attack made on military engineers and military engineering, as un- 

 called for and unprovoked, as it is narrow-minded, illiberal, and un- 

 gentlemanly, and I am sure that from a sense of justice you will insert 

 these few remarks in reply to the anonymous libeller who signs him- 

 self " Civilian." ' 



The purport of the writer is an evident desire of venting his petty 

 spleen on a body of talented, high-minded, and honourable men, and 

 wdiilst I much regret that your columns have been made use of for the 

 purpose of libelling a "Captain of engineers at the head of the archi- 

 tectural and engineering departments of the Admiralty," viz. Captain 

 Brandreth — a gentleman whose talents, urbanity and kindness have 

 endeared him and made him respected by all who have been connected 

 with him in his professional capacity — I'Lim sure that no civil engineer 

 laying the slightest claim to station," to gentlemanly feeling, or to re- 

 spectability, would ever descend to such low personalities, nor will 

 " Civilian " ever obtain the sanction or countenance of such men to his 

 vituperations. 



If "Civilian" had the benefit and the interest of the civil engineer 

 at heart, he would never for a moment wish to weaken the union 

 which is now daily increasing between the civil and the military engi- 

 neer, for their mutual as well as for the public good. The spheres of 

 action of the two professions lie in almost every case so widely apart 

 that they may be said never to clash; while the foreign services of 

 the military engineer open to him a vast field of inquiry and infor- 

 mation, which those who practice in this country as civilians are un- 

 able to obtain. His varied information, his experience, strength of 

 mind, and coolness for calculation, fully entitle him to such offices as 

 the country is able to give; and in justly awarding the few she does 

 to him, she but acts for her own interest. 



With respect to young gentlemen who are educated at the military 

 colleges — is "Civilian" aware of the rigid examination these gentle- 

 men have to pass through before they are entered into the corps of 

 engineers? and that but a very small number are admitted into Ihal 

 corps every year ? Is he also aware of the number of young gentle- 

 men who are annually sent out of engineers' offices, after spending, 

 as "Civilian" boasts, "nearly £1000," is he awaie that ihey are sent 

 out without a7ty ixaminalion, and in most cases with a meagre know- 

 ledge picked up in the best way they are able, and not " drilled under 

 the auspices of their colonel" — would they had been I And why, I 

 would ask, are men of talent, of exertion, of experience, not to prac- 

 tice in the varied callings of their profession, if they so please, if they 

 are competent, and if the public will employ them? 



I am a civil engineer myself, which fact I doubt of " Civilian," in- 

 deed I would not, for the credit and the respectability of the profes- 

 sion, believe he ranked himself as one, as no man holding any station 

 in it, much less having any respect for himself, would be the author of 

 such a production. 



I am, Sir, 



Your obedient servant, 



Bristol. Veritas. 



SLATE CHIMNIES. 



Sir— Having lately adopted a plan, by means of which slate slabs 

 may be made use of, in the construction of chimneys or flues, in con- 

 nexion with an open fire grate, and in situations where the common 

 brick chimneys could not be built, I take the liberty of submitting the 

 plan to your consideration. 



Having not long ago taken possession of a house, attached to which 

 was a room built at the side, and not having fire place and chimney I 

 adopted the following plan : — I fixed to one of the walls of the room, 

 at a proper height from the floor, a common open fire-basket or grate, 

 having a strong iron back, not let into the w'ull, but fixed in front of it. 

 I then had four long narrow slate slabs put together, so as to form a 

 square hollow pillar open at top and bottom, and the pillar so formed 

 I had erected against the -.vail immediately over the fire-grate, and 



