APPENDIX, 



261 



The apparatus descriVjed in the following' pages will give warning, by the 

 ring of a bell, when an exposed thermometer has fallen to a given tempera- 

 ture, and can be placed anywhere in the orchard or field. The other parts 

 can be put in the house with the warning bell in a convenient place. The 

 entire cost of the apparatus is from $.1 to $"• From the following description 

 any electrician can make the apparatus, and a person not acquainted with 

 electrical methods can put it in place. 



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Fig. 1— Electrical apparatus. 



DESCRIPTION OF APPARATUS. 



The apparatus consists of a battery, relay coil, alarm bell, and thermome- 

 ter. The battery used is the common crow^foot cell used in telecfraphing, 

 size six inches by eight inches. 



The relay C (Fig. 1) is composed of two coils. Each coil has an iron core 

 one and one-fourth inches long, one-fourth of an inch in diameter, and is 

 wound with No. 2-4 B. and S. double cotton-covered magnetic wire, to a depth 

 of one-fourth of an inch. The coils are wound right and left-handed and 

 are placed horizontally. 



The armature A consists of an upright piece with a crossbar of soft iron, 

 which is so held that it is attracted by the iron cores of the coils when mag- 

 netized. An adjustable spring holds the armature A against the screw S, 

 when no current is flowing through the coil C. The maker should put on 

 the base of the coil binding-posts marked with the connections as given in 

 Fig. 1. A fifty-cent doorbell will answer for the alarm. 



The thermometer consists of a glass stem eight or ten inches long, with 

 an internal diameter of approximately one -twenty-fifth of an inch ( one cen- 

 timetre ) attached to a bulb which has a diameter of one inch ( twenty-five 

 centimetres ). The bulb and two or three inches of the lower part of the tube 

 are filled with mercury and the tube is graduated for every ten degrees from 

 30° F. to 100° F. Electrical connection with the mercury is made by a plat- 

 inum wire blown in the glass. On the top of the stem is a brass cap with a 

 No. 30 B. and S. bare copper wire passing through it and making contact 



