... Correspondence ...

Progress, Volume I, Issue 7, 1 May 1906, Page 182

... Correspondence ...

[Readers are directed to the rules set out in " Business Notices " on page 183.]

P.N., Invercargill. — The claim made by the Westinghouse magnetic brake for an equal efficiency, whether the car be running at 2 miles or 20 miles an hour, is purely a relative one, as you will ascertain from the particulars which appeared in December issue of Progress. This brake is intended to arrest the speed of the car in case of emergency, although it is commonly used where high speed and perfect control are required in street traffic. Recourse to the hand ratchet brake for actually stopping the car is necessary after the magnetic brake has done its work. Once the wheels stop, the magnetic brake is powerless, for the reason that the rotating action of the wheels causes the motors to be transformed into generators which electro-magnetise the shoe brakes, and automatically apply them. The motorman operates the magnetic brake by simply reversing the handle of the controller. There is no doubt improvements are possible with all existing forms of brakes. Mr. W. G. T. Goodman, of Messrs. Noyes Bros., Dunedm, would perhaps be pleased to give you further particulars of the \\ estmghouse magnetic brake. 8.H.8., Mangorei — The matter you complain of was evidently an oversight which can be rectified at some future date. W.N.A., Wellington — The price asked is Write the owner whose address is given in his advertisement. Motor Boat Auckland. — The design of boat will depend on the work it has to do, and whether sea or river going. With a length of 33 ft only, the beam would need to be considerable to carry 1=; tons, and leave good room for the engine etc. To drive a boat of this size 12 miles per hour a foiir-cylmdered engine, 4m. by 5 m., would be powerful enough. This can either be made to use petrol or paraffin and with high tension ordinary or magneto ignition. The h.p. would be about 20 You had best get the boat built to suit your work and you can then easily adapt the motor to suit.

H.P , Chrisi church. — A kilowatt is 1,000 watts, or i^- h.p. Electric h.p. is 746 watts. 'Phone. — A tube core for induction coil will not be quite so sensitive to rapid and delicate variations in the current as one built up of iron wires • and the presence of the brass rod through its centre will, by diminishing the mass of iron by about a £ also lower its efficiency to some extent. Tempus. — The simplest way to get exact time is to observe the crossing of the meridian by the sun's centre, and apply corrections for longitude and equation of time, the latter from an almanac A transit instrument fixed accurately in the meridian is necessary. Exact time at any part of the day may be got from the sun's altitude by means of a sextant and artificial horizon. Magnet. — If you can beg, borrow, or steal, or in the public library get a chance of reading one or all of the following books, you will learn as much as is known on the subject — viz., Deschanel's " Electricity and Magnetism," Ganot's '' Physics," by Atkinson, Silvanus Thompson's " Elemental y Electricity and Magnetism."