(71) To Find the Cubic Content of Irregular Spaces. a m b The cubic content of irregular solids is most conveniently obtained by applying Thomas Simpson's formula for finding the area of an irregular curvilinear space. To the sum of the extreme sections add four times the sum of the middle or mean sections, and twice the sum of the given intermediate sections: this sum multiplied by one-third the common distance between any section and the next middle section equals the cubic content. This will be found a useful rule for finding the capacity of old-fashioned drains and similar channels. Thus to borrow an example from Tate's geometry. Required the content of a drain, see Fig. 16, whose cross sections taken at 30 feet apart are as follows: the top breadths ab are 4, 3, and 5 feet, the corresponding depths are 3, 2, and 4 feet, and the breadth de at the bottom 2 feet, being the same for every section of the drain. Here the sections are all trapezoids; hence we have area of 1st section (4+2) × 3 = 9; area of 2nd section, (3+2) × 2 = 5; area of 3rd section, 1⁄2 (5 + 2) × 4 = 14 ; FIG. 16. (72) Example of Reports on Ventilation. A report1 by the late Professor de Chaumont on the ventilation of a barrack room, will serve as an example of the kind of report which should be made by a sanitary officer if in any case he should be called upon to make a detailed and scientific examination of ventilation. 1 Army Medical Department Statistical and Sanitary Report, vol. vi., 1864. Nov.15th, 1865, 1a.m., Room 2, G battery, over the stable, intended for 25 men, 21 men actually occupying it. Length, 40 feet; breadth, 28 feet; height, 10.5 feet. Gross cubic space. Cubic Feet. 11,343 which gives for 25 men (11,327 cubic feet), per man, 453 cubic feet; for 21 men (actual number) 540 cubic feet. Ventilation-Inlet Acting. One stove louvre, 130 square inches; 1'25 × 2′′16 ( taken). Rate of movement not measurable; no fire. Outlets. Two shafts (10" X 10"), opening obstructed by a board, only taken in consequence, rate not measurable One chimney Inlet Total outlet Total inlet and outlet This gives for 25 men 9.6 sq. inches per man; for 21 actual discharge by chimney, 10,433 cubic feet per hour. stables. 50 square inches. 60 93 Carbonic Acid. 1.028 in 1,000 volumes. 2 )2.155 1.077 Dry bulb, 60°5; wet bulb, 59°5; Dew point, 58° 15. Elastic force of vapour, *493. Weight of vapour in a cubic foot of air, 55 grains. Additional weight of vapour required to saturate the air, 4 grain. Humidity (saturation 100) 94. At 3:50 a.m.; Dry bulb, 58°; wet bulb, 56°. Dew point, 54°2; Elastic force of vapour, 421; Weight of vapour in a cubic foot of air, 47 grains; Additional quantity required to saturate the air 7 grain; Humidity, 87. On the 16th November, 11 p.m. :-Smell Close. Carbonic acid 804 in 1,000 volumes. Dry bulb, 60°; wet bulb, 57°. Dew point, 54°4. Elastic force of vapour, 423. Weight of vapour in a cubic foot of air, 477 grains. Additional quantity required to saturate the air, 10 grain. Humidity, 82. To briefly indicate how each of the observations are obtainedcubic space and measurement of areas generally by actual measurement on principles detailed on pages 104-111. Movement of air, by an anemometer. The anemometer used for the purpose of ascertaining the velocity of currents of air, essentially consists of small very light mica sails set in a metal frame; these turn on an axis, furnished with an endless screw, which again turns a clock-work train, moving needles, which travel round properly divided circles and register the velocity. Of these anemometers there are various forms, one of the best is made by Mr. Casella, and contains improvements suggested by the late Dr. Parkes. The graduations for each instrument are obtained by actual experiment by means of machinery made for that purpose, so that the indications of all are as comparable with each other as the weight or measure of ordinary substances. The indications are shown by means of the large dial and hand and five smaller ones as shown in the annexed plate. The whole circumference of the large dial is divided into 100 parts, and represents the number of feet up to 100 traversed by the current of air. The five smaller dials are each divided into 10 parts only, one revolution of each being equal to ten of the preceding dial, and represents 1,000, 10,000, 100,000, 1,000,000, and 10,000,000, respectively. By means of the large dial, the low velocity of 50 feet per minute may be measured, and by the smaller ones continuous registration is extended up to 10,000,000 feet, or equal to 1,893 miles, being practically beyond what the most extended observations can require, whilst jewelling in the most sensitive parts insures the utmost delicacy of action. By moving the small catch a backwards or forwards, the work is put in or out of gear, without affecting the action of the fans; this prevents the injurious effect of stopping them suddenly, and enables the observer to begin or end his observations to a second. A small handle with universal joint accompanies the instrument, and may be screwed in at the base; by putting a stick through this, it may be raised or lowered to any required height, and used in any position. A table accompanies each instrument by means of which allowance may be made for the difference caused by inertia at high and low velocities. Carbonic acid, by the method detailed on page 97. The dew point, calculated from the difference between the wet and dry thermometers, or obtained directly from Dynes' hygrometer. Elastic force of vapour, the number is found, as described at p. 129, opposite the number for the dew point. Weight of vapour in a cubic foot of air, is obtained from Table XXIII. p. 133, opposite the dew-point temperature. Additional weight required for complete saturation by taking out the number indicating the weight in grains of moisture to completely saturate the air at the temperature of the dry bulb, and then subtracting the weight of vapour already found from the table actually in the air, as shown by the dew-point. Humidity from tables or by dividing the weight of vapour actually found by the weight of vapour, which, if the air was saturated, it would have contained, saturation being considered 100'. Thus, in the example on page 113— Weight of vapour in cubic foot of air 4.77 × 100 |