Popular Science Monthly 



913 



Determining the Intensity of Illumination 

 by a New Measuring System 



ANEW and cun\eniont type of instru- 

 ment for the measurement of light lias 

 been developed by Norman Macbeth, 

 illuminating engineer. It differs from the 

 photometer, an instrument some- 

 what similar, only in the details 

 of its construction and in that 

 its scale is calibrated to read in 

 foot-candles. But the method 

 of its use is ditYerent. 



To measure illumination in- 

 tensities a test-plate, made of 

 white material of good diffusing 

 qualities, is placed at tlie point 

 in the plane where the illumina- 

 tion value is desired. It becomes a sec- 

 ondary source of light, the brightness of 

 which is compared with that of a trans- 

 lucent screen, the measuring instrument 

 of which is illuminated to a known intensi- 

 ty by a small tungsten lamp. 



The intensity of any source of illumina- 

 tion may be determined by placing the test- 

 plate a known distance from the source, 

 measuring the illumination-intensity in 

 foot-candles upon the test-plate and then 

 computing the candlepower by multiplying 

 the scale values by the square of the dis- 

 tance of the test-plate from the unknown 

 source (the law of inverse squares). 



The scale is calibrated in foot-candles 

 and the readings give the intensity of 

 illumination at a given point. 



The registers are 

 provided with water- 

 pans to moisten the air 



Deflecting and Moistening the Air 

 from Furnace Registers 



UNTIL wc substituted the modern hot" 

 air furnace for the stove we did not 

 know what a completely warmed house 

 was during the winter months. But evil 

 accompanies good. The heated 

 air from the furnace is too dry 

 for good health and perfect com- 

 fort, and as an additional worri- 

 ment, the walls at the sides and 

 above the registers soon become 

 discolored by the blackened dust 

 which riscsand disperses through 

 the rooms of the house whenever 

 the ashes are shaken down or the 

 furnace cleaned. 

 To obviate these troubles a register-shield 

 has been placed on the market, which may 

 be inserted over either floor or wall registers. 

 These metal shields deflect the rising stream 

 of hot air and direct it out into the room 

 instead of allowing it to go directly toward 

 the ceiling, as it otherwise would. The 

 shields are also provided with water-pans 

 which are kept warm by the air from the 

 furnace. The water evaporates and moist- 

 ens the air as it passes through the shield. 



A^ 



Removing Old Starch from Clothes by a 

 Malt Extract Bath 



S starch is insoluble in water it has 

 always been a hard problem of the 

 laundrjman to remo\e it from soiled col- 

 ars, lace curtains or other arti- 

 cles which are either heavily 

 starched or made from delicate 

 material. 



Strong, hot alkaline baths and 

 long rubbing or pounding have 

 been the principal resort, al- 

 though they shorten the life of 

 the fabrics, destroying wool 

 fibers, shrinking cotton and 

 spoiling colors. 



Modern laundries are begin- 

 ning to introduce the malt ex- 

 tract bath as a substitute for the 

 alkalies in laundries. Malt is a 

 chemical compound ha\ing the 

 property of converting starches 

 or starchy foods into soluble 

 dextrine or glucose. It requires 

 only four ounces of malt extract 

 to remove the old starch from 

 one hundred collars or an equiv- 

 alent amount of goods, and it is 

 not aftected by hard water. 



The lamp 

 carriage is 

 moved up 

 and down in 

 the tube by 

 means of a 

 rack and 

 pinion oper- 

 ating upon a 

 brass rod 



The aperture 

 opposite the 

 telescope is 

 pointed to- 

 ward the test- 

 plate or any 

 surface 

 whose bright- 

 ness is to be 

 measured 



