AUTOMATIC VENTILATION. 



NUMBER of letters 

 have been sent to 

 the editor of The 

 American Garden 

 asking for more in- 

 formation concern- 

 ing the automatic 

 greenhouse erected 

 by Mr. Charles Bar- 

 nard, of Stamford, 

 Conn., and in an in- 

 terview Mr. Bar- 

 nard gave further particulars of his experiments. 



"We first took out one of the lights of the middle 

 sash, and over this opening placed the wooden trunk 

 and chimney described in the October number of 

 The American Garden. At first we had no valve as 

 seen in the illustration on page 6ii, and in place of 

 this we had a metal valve, taken from the top of an 

 old incubator. The first e.xperiments were with ap- 

 paratus already used to ventilate the incubator. We 

 took the entire apparatus — thermostat, cranks, 

 rods, valve and connections — from the incubator, 

 and by turning them around in another position 

 fitted them to the underside of our ventilator. The 

 thermostat was of the rod type, the rod being cov- 

 ered with rubber. We made a new frame for the 

 rod, and then hung it just under the glass at one 

 side of the ventilator. It was then an easy job to 

 connect the bar with the arm that operated the valve, 

 and once set up, the apparatus worked to perfec- 

 tion for many weeks without a single failure. 



' ' The whole thing was simply an automatic ventil- 

 ator taken out of an incubator and fitted to a green- 

 house. Of course, the house was many times lar- 

 ger than the incubator, and it would seem impos- 

 sible to use it to advantage. Practical, daily ex- 

 perience through many weeks showed that it would 

 do the business. It can be explained in this way. 

 The thermostat (as in all incubator thermostats) 

 could be adjusted to various temperatures, and we 

 set it to operate in the full sun at the very top of the 

 house at 80° Fahr. It proved to be very sensitive, 

 and the valve began to open very soon after the sun 

 shone upon the thermostat. At 85° the ventilator 

 was wide open. At 83° it would begin to close, and 

 at 79° it was closed tight. 



" The result was that the heat was released the in- 

 stant the house became too warm, and the warm air 



went out in a swift and steady stream all the time 

 the ventilator was open. The smoke from a lighted 

 match held at one end of the house would travel 

 along under the glass and curl up into the ventil- 

 ator, while a candle flame held near the ventilator 

 would be bent out of shape and lay horizontal with 

 the point to the ventilator. The secret of the suc- 

 cessful working of such a small ventilator seemed 

 to be in the tall chimney over the valve. No cold 

 air could get down into the house, and the hot air 

 was swept out as fast as it gathered. A passing 

 cloud would cause the ventilator to close, and it 

 would open again within two minutes of the return 

 of the sunshine. The thing was a real and practi- 

 cal automatic ventilator, and kept the house at an 

 even temperature for many weeks without attention. 



If two or, perhaps, three such ventilators had 

 been put in we would have had no further trouble. 

 In February the sun became so powerful that the 

 heat would accumulate faster than the ventilator 

 could carry it off. We then made a larger opening 

 in the glass and put in a larger chimney with the 

 valve shown on page 611. To operate this valve 

 we made a thermostat according to the following 

 description taken from the Scientific American.'' 

 (See Figure i.) 



' ' The instrument depends for 

 its operation on the difference 

 between the expansion of bra.= s 

 and steel. The linear expan- 

 sion of brass is nearly double 

 that of steel, so that when a 

 curved bar of brass is confined 

 at the ends by a straight bar 

 of steel, the brass bar will elon- 

 gate more than the steel bar 

 when both are heated, and will, 

 in consequence, become more 

 convex. 



"At 2 are shown two bars, 

 the straight one being of steel, 

 the curved one of brass. The 

 steel bar is slit for a short dis- 

 tance in two places at each 

 end, and the ears thus formed 

 are bent in opposite directions 

 to form abutments for the ends 

 of the curved brass bars, two brass bars being held 

 by a single steel bar, thus forming a compound bar, 



1 



Fig. I. 

 Details of the 

 Thermostat. 



