April 4, 1890.] 



SCIENCE. 



223 



manJ for them, but against the adoption of manual training as a 

 part of the general eJueational course. At the close of the dis- 

 cussion one of the members moved that a committee of the asso- 

 ciation be instructed to define the term '-manual training," which 

 would certainly seem to be a proper and even necessary thing to 

 do, if there is ever to be an agreement about the expediency of 

 such training. Bui the motion raised a perfect storm of opposi- 

 tion, so that the chairman had to interpose a few remarks to pre- 

 vent an acrimonious dispute. Another important subject treated 

 was that of examinations, especially the examination of teachers, 

 which was recognized as at once a work of great importance and 

 of great difficulty. Candidates for the position of teacher are 

 now often examined by persons with no real fitness for the task, 

 and some remedy for this evil is undoubtedly necessary. Besides 

 these topics, the assembled superintendents discussed the training 

 of teachers, the duties of principals, and other themes that need 

 not be specified here. 



LETTERS TO THE EDITOR. 



*** Correspondents are requested to be as brief as possible. The writer's name 

 is in all ca^es required as proof of good faith. 



The editor will be glad to publish any queries consonant with the character 

 of the journal. 



On requests twenty copies of the number containing his communication will 

 be furnished free to any correspondent. 



Heat and Ventilation. 



In your issue of Feb. 38 is a notice of the Timby system of 

 heating and ventilation, which, you say, " is now attracting uni- 

 versal attention, especially in New England." It is to be hoped 

 that New England will not miss the delicate touch of flattery 

 perhaps unconsciously given her in this quotation, and that your 

 columns are open to any voice of intelligent response which may 

 come back from her. 



The attention of which you speak is not stated to be that of 

 competent engineers, nor that of others better qualified than "ex- 

 mayors " to judge of the merits of the described system. It is not 

 defined as that of either scientific sanction or condemnation. 



But the appearance of the article in Science, and wi'^hout un- 

 favorable comment, would seem to the popular mind to lend a 

 quasi-scientific approval to the enterprise, as it doubtless has af- 

 forded gratification to its promoters. 



The art of ventilation has suffered much injury at the hands of 

 many whose ingenuity has not been the well-trained servant of a 

 sound scientific knowledge. The field is a fertile one for the cul- 

 ture of schemes and methods more visionary than practicable, and 

 more gratifying to inventors than profitable to users. To protect 

 the public against imposition, to save the popular mind from dis- 

 couragement through repeated and costly failures, to expose and 

 weed out the worthless methods from the good, and to establish 

 popular faith by evidence of actual or possible success in any 

 worthy undertaking, is a legitimate and laudable service for any 

 man or journal capable of rendering it. 



To this end it would afford satisfaction to see in your columns 

 a thoroughly trustworthy discussion of the applicability of the 

 Timby system to the actual necessities of good ventilation and 

 heating. With a view to eliciting contributions to such a discus- 

 sion, the following propositions are submitted : — 



First, The mechanical part of the problem is beset with insu- 

 perable difficulties of various sorts, some of which are closely akin 

 to those belonging to the long ago demonstrated impracticable 

 scheme of ventilating a city's sewers by a centrally located sys- 

 tem of pneumatic exhausters. 



In the company's pamphlet, and under the head of " Flan of 

 Introduction," the statement is made that it is proposed to heat 

 and ventilate a town of 50,000 inhabitants by means of one cen- 

 trally located plant. 



The first essential in ventilation is an adequate air volume, and 

 the second is an effective use of it. If the dermal and thoracic 

 excretions are to be diluted to one in two hundred, — a proportion 

 of diluent which for the pelvic excretions would be considered far 

 too small to fit them for potable or edible use, — the air-supply 

 for such a town should be 1.50,000,000 cubic feet per hour ; and 

 for the sweetening of the 2,000 buildings of 30,000 cubic feet ca- 



pacity each, in which the inhabitants may, for the purposes of 

 computation, be supposed to compactly live, the air-sujiply should 

 reach at least that quantity. Let it be reduced to 100,000,000, 

 and, for the sake of simplifying the mechanical problem, let the 

 houses be ranged along two intersecting streets, 500 houses to 

 each half-street, and let the ventilating plant be located at the 

 point of intersection. Let the houses stand in compact block 

 form, and average, with alley and cross-street spaces, forty feet 

 frontage. Let each of the main air-conduits be six feet in diame- 

 ter, and the central supply-shaft twelve feet. The velocity of air^ 

 flow through the main conduits would be nearly 15,000 linear feet 

 per minute, and the theoretical power required to propel the air 

 would be about 125,000 horse-power, 4,000 being required to give 

 the air its initial motion, and the balance to overcome the resist- 

 ance of friction. This computation takes no account of the fur- 

 ther work required for moving the air through leads to the 2,000 

 buildings, and through the ramifying conduits for its distribution 

 to their several floors and rooms. 



The above computations are qualified as theoretical, since it is 

 assumed that the efficiency of the motile machinery employed is 

 unity instead of the one-third cir one-fourth usually available in 

 such mechanism. It would be interesting and instructive to ex^ 

 amine a description of the apparatus it is proposed to use for the 

 propulsion of such large volumes of air under the liigh pressure 

 demanded. To effect the pressure by blowers, the velocity of 

 their blade tips would have to exceed that of a rifle-shot, and a 

 twenty -foot diameter fan must make the quite impossible per- 

 formance of 1,800 revolutions per minute. 



Let the question be simplified to that of supplying air to two 

 such buildings as the newer ones of the Massachusetts Institute of 

 Technology, they monopolizing an entire main, and being located 

 at its extremity. The theoretical horse-power requii-ed would be 

 some 345, agairst a present actual mean of 15 or so, for the supply 

 of 5,600,000 cubic feet of air an hour. 



Second, The method proposed for warming the air supplied 

 through the mains by means of a hot-water pipe with return 

 bend, as shown in the cut reproduced by Science, and described in 

 the company's pamphlet, is defective. 



The pamphlet states that the pressure within the pipe is not to 

 exceed five pounds, and that the heat-loss in the water is not to 

 exceed five per cent. The statement, though somewhat ambigu- 

 ous, may reasonably be made to mean that the water starting 

 with a temperature of 227" will return to the heater cooled 

 through 12". 



If the sole aim of this warming of the air were to raise it to the 

 temperature of comfort, say 70°, before supplying it to the build- 

 ings, and the matter of heating the buildings were excluded from 

 consideration, the volume of water to be moved through the pipe 

 would, on a day of average winter temperature, be nearly 200,000 

 gallons an hour, or a flow rate of nearly five miles an hour through 

 a fourteen-inch nipe. 



For extreme weather this quantity must be more than doubled, 

 and, if the heating of the buildings is to be included, the duty of 

 the heating system must be quadrupled. 



A study of the mechanical part of this heating problem is not 

 here presented. 



Presumably the small fraction of the exhaust steam from the 

 air and hot-water pi'opelling engines required for heating pur- 

 poses would be utilized. Enough would still remain for the com- 

 fortable heating of some halfscore of adjacent towns of rival 

 size. 



A description of the arrangement of the proposed pipe or other 

 heating surface, so that cumulative heating effect should be 

 avoided, and a uniform temperature maintained throughout the 

 mains, would interest many of your readers. 



Third, The required inequalities of temperature in the air-sup- 

 ply to various buildings, and to the various parts of the same 

 building, cannot he furnished from one supply source maintained 

 at a fixed temperature. 



For the shady or the windward side of a dwelling whose air is 

 "changed" but once an hour, the air-supply temperature may need 

 to be in gome weathers IGO" cr 200''; and on the sunny or the 

 leeward side, or in the sleeping or sick room, twenty to thirty dt- 



