Excerpt: ...those supplied with a powerful electric torch; and this arrangement is actually used to some extent by travelling lecturers, but the mess and trouble of keeping the accumulators in order have prevented the method being generally adopted. When alternating current is available such a lamp will work well with a transformer to step down the voltage to the required degree, and the arrangement is simple, cheap, and efficient, and produces a light at least equal to that from 43 acetylene. In comparatively small halls, ...
Read More
Excerpt: ...those supplied with a powerful electric torch; and this arrangement is actually used to some extent by travelling lecturers, but the mess and trouble of keeping the accumulators in order have prevented the method being generally adopted. When alternating current is available such a lamp will work well with a transformer to step down the voltage to the required degree, and the arrangement is simple, cheap, and efficient, and produces a light at least equal to that from 43 acetylene. In comparatively small halls, where the current is alternating, this is undoubtedly the best method of working, as it is simpler than the arc and amply brilliant enough for all practical purposes. With the continuous current the problem is not so simple, as transformation of voltage is not an easy matter, and a glow-lamp on; say, a 200-volt circuit involves a long and fragile filament, which it is difficult to arrange in a small space. Many years ago the Ediswan Company produced a 'Focus' lamp for the purpose, with the filament arranged in the form of a square grid, and this lamp gave a light of about 100 candles, and was fairly successful for a small room. More recently the Osram Company introduced a similar lamp with a metal filament arranged somewhat in the form of a cone, and this lamp also sufficed for a small class-room. It was, I believe, made in Germany and was practically unobtainable during the war. I understand the Osram Company are at present arranging to manufacture it in this country, but up to the time of writing it has not made its appearance. None of these lamps worked direct on a public lighting circuit can be regarded as really satisfactory, as it has been found impossible so far to get a concentrated light; the 100-volt lamps have, of course, been superior to those made for 200 or 250, but they are all for lantern purposes far behind low voltage lamps, which are really good when a suitable current can be obtained. The Pointolite Lamp.
Read Less
Add this copy of Optical Projection: a Treatise on the Use of the to cart. $18.05, good condition, Sold by Books From California rated 4.0 out of 5 stars, ships from Simi Valley, CA, UNITED STATES, published 1906 by Longmans, Green and Co.
Choose your shipping method in Checkout. Costs may vary based on destination.
Seller's Description:
Good. Ex-library copy with usual markings. Cover and edges shows shelf wear. Pages are clean and intact. Very Clean Copy-Over 500, 000 Internet Orders Filled.
Add this copy of Optical Projection: A Treatise On the Use of the to cart. $22.29, new condition, Sold by Ingram Customer Returns Center rated 5.0 out of 5 stars, ships from NV, USA, published 2022 by Legare Street Press.
Add this copy of Optical Projection a Treatise on the Use of the Lantern to cart. $25.83, new condition, Sold by Paperbackshop rated 4.0 out of 5 stars, ships from Bensenville, IL, UNITED STATES, published 2018 by Forgotten Books.
Add this copy of Optical Projection a Treatise on the Use of the Lantern to cart. $29.15, new condition, Sold by Paperbackshop rated 4.0 out of 5 stars, ships from Bensenville, IL, UNITED STATES, published 2013 by Hardpress Publishing.
Add this copy of Optical Projection: A Treatise On the Use of the to cart. $33.45, new condition, Sold by Ingram Customer Returns Center rated 5.0 out of 5 stars, ships from NV, USA, published 2022 by Legare Street Press.
Add this copy of Optical Projection: A Treatise On the Use of the to cart. $35.34, new condition, Sold by Ria Christie Books rated 5.0 out of 5 stars, ships from Uxbridge, MIDDLESEX, UNITED KINGDOM, published 2022 by Legare Street Press.
