392 SCIENTIFIC EECORD FOR 1882. 



The details of the apparatus are as follows: At the summit one of Dr. 

 Siemens's electrical thermometers (kindly placed at the society's dispo- 

 sal by Messrs, Siemens, Bros. & Co.), and an ordinary thermometer are 

 mounted in a small screen fixed to one of the pinnacles of the tower; 

 on the roof of the belfry, which is 170 feet above the ground, a Steven- 

 son screen has been mounted, containing maximum, minimum, dry, and 

 wet bulb thermometers. In the church-yard another Stevenson screen 

 has been fixed containing a similar set of thermometers, for comparison 

 with those above. All the thermometers will be read every morning at 

 nine o'clock. The electrical thermometer consists of a coil of wire wound 

 round a cylindrical piece of wood inclosed in a small brass tube; a third 

 wire is joined to one of the wires ; and the three, insulated by gutta-per- 

 cha, form a light cable which is brought down to the base of the tower 

 and connected to a galvanometer, the terminals of which are in connec- 

 tion with the two poles of a six-cell Leclanche galvanic battery. The 

 instrument is read by depressing a key, which causes the needle of the 

 galvanometer to deflect; a pointer vernier (moving a contact roller upon 

 a wire in a circular groove) is then pushed to the right or to the left 

 upon a divided scale until the needle remains stationary on the zero 

 point, when the electrical resistance of the wire is measured upon the 

 scale. The number indicated by the vernier is then read off, and by re- 

 ferring to a table of equivalents the actual temperature in degrees of 

 Fahrenheit is readily ascertained. Simultaneous readings of the elec- 

 trical thermometer at the summit of the tower and of the dry-bulb ther- 

 mometer in the church-yard will be made frequently during the day by 

 the verger of the church. (iVWwre, xxv, p. 470.) 



Siemens describes the deep-sea electrical thermometer used by the 

 Coast Survey in recent researches. This is, he states, a modification of the 

 apparatus suggested by himself in 1871 and used by Weiuhold for high 

 temperatures in 1873. The observations made with it by the Coast Sur- 

 vey in the summer of 1881 have every indication of being more accu- 

 rate than those made with the protected Miller-Casella thermometers. 

 About five minutes are required to enable the resistance coil to assume 

 the temperature of the water surrounding it, and a second period of 

 five minutes is needed for adjusting the temperature of the comparison 

 coil on deck. (Similar apparatus can of course be used for measuring 

 underground temperatures, as has indeed been done by Becquerel at 

 Paris.) Siemens's apparatus consists of a coil of silk-covered iron wire 

 .15°"° diameter, and about 432 ohms resistance, attached to an insu- 

 lated cable by which it can be lowered to the required depth, and con- 

 nected so as to form one arm of Wheatstone's bridge. The correspond- 

 ing arm of the bridge is formed by a second coil made precisely similar 

 to the former one and of equal resistance. This coil is immersed in a 

 copper vessel filled with water, and the temperature of the water is 

 adjusted by adding iced or hot water until the bridge is balanced. The 

 temperature of the water in the vessel is then read by a mercurial ther- 



