August 15, 1884.] 



SCIENCE, 



131 



in the lectures. Alongside the latter is a port- 

 folio case (PC) for the diagrams and drawings 

 required in the same courses. Near the large 

 case in the laborator} 7 is the structure familiarly 

 known as the ' tower,' but called the inter- 

 rupter-case (IC) in the plan, which has been 

 found to be a great convenience. A view of 

 the upper portion of the tower is given in fig. 4, 

 the lower part being merely a large closet for 

 wire and other supplies. Its purpose is to hold 

 various pieces of apparatus for interrupting or 

 regulating the galvanic 

 current. As a rule, 

 all the batteries made 

 use of in the laboratory 

 are set up as required 

 in the battery- closet in 

 the gallery, and con- 

 nected with wires run- 

 ning to the tower, 

 whence the current is 

 conducted to the appa- 

 ratus, or to wires run- 

 ning into the rooms 

 where electricity may 

 be needed, as well as 

 to the lecture- table. 

 The general relation of 

 the wires to the bat- 

 tery - room and the 

 tower is shown in the 

 plan of the gallery (fig. 

 2). A special line of 

 very large copper wires 

 is also shown, which 

 goes directly, without 

 a break, to the remoter 

 work-rooms. This line 

 has been found neces- 

 sary for the battery re- 

 quired to work a large 

 Euhmkorff coil at that 

 distance. The pres- 

 ent system of wires has 

 been planned chiefly to 

 meet the demands of 



ordinary work, but is capable of such exten- 

 sion as may be required. Outside the tower 

 hangs the seconds pendulum (SP) , which is 

 heavy enough to swing for about half an hour. 

 It can be put in any circuit, and thus give 

 very exact time or regular interruption in any 

 room of the department. In the tower itself 

 the only pieces of apparatus considered per- 

 manencies are those seen in fig. 4, — a clock 

 and a new interrupter, recently imported from 

 Leipzig. The latter rather complicated in- 

 strument seen on the left of the figure has 



Fig. 4. — Interrupter-case. 



valuable features ; the platinum contacts be- 

 ing under alcohol or petroleum, and so arranged 

 that either the closing or opening induced cur- 

 rent may be short-circuited. The rapidity of 

 the shocks can be considerably varied within the 

 limits of thirty in one second, and one in thirty 

 seconds. This apparatus was constructed by 

 Baltzar. In principle it is the same as that 

 described by Bohr, in his article, " Ueber den 

 einfluss der tetanisirenden irritmmente auf form 

 und grosse der tetanus curve " (Arch. anat. u. 

 physiol.,physioL abth.. 

 1882, p. 233). Many 

 changes have, how- 

 ever, been made in the 

 details before the pres- 

 ent form was arrived 

 at. In this a metal- 

 lic cylinder turned by 

 clock-work carries two 

 sets of pegs (like the 

 pins in a musical box) , 

 which strike against 

 levers, and thus break 

 contacts in the trough 

 below. The pins of 

 each series are so set 

 that the contact is 

 broken in one lever a 

 little sooner than in 

 the other, and conse- 

 quently is still broken 

 in the latter when the 

 former closes. In this 

 wa} T a simple change of 

 the wires from the in- 

 duction apparatus per- 

 mits the short-circuit- 

 ing of the opening or 

 the closing induction 

 shock at pleasure. By 

 an ingenious arrange- 

 ment a cog-wheel can 

 be shifted so as to give 

 the cylinder a very 

 slow or a rapid motion, 

 as desired : the series of pegs thus do double 

 work, and permit the great range of inter- 

 ruptions already mentioned. 



The clock, seen on the right of the figure, 

 has a revolving pendulum, and a set of toothed 

 wheels, which interrupt the electric current at 

 intervals of one, two, three, four, five. ten. 

 fifteen, twenty, thirt}', or sixt} T seconds. The 

 duration of the interruptions ma}' be any thing 

 less than four seconds. By using a relay these 

 may be changed into closures of correspond- 

 ing length and interval. This clock was con- 



