30 BULLETIN OF THE LABORATORIES 



currents (say lo to 15 amperes) through low resistances. It has 

 the additional advantage of requiring absolutely no attention for 

 many months when once put in operation, no handling of strong 

 corrosive acids in setting it up, and a minimum of labor and in- 

 convenience in renewing the zincs. 



We have had in operation in our laboratory for several years 

 three modifications of this cell arranger: one with plugs connect- 

 ing brass blocks mounted on a vulcanite plate, another with the plugs 

 replaced by sliding switches of spring brass, a third having the brass 

 blocks replaced by screw cups connected by short wires. The 

 instrument with plugs is surest in its contacts and quick in op- 

 eration, but the most expensive of the three ; the second is quick- 

 est in operation, the third simplest in construction. 



If constancy for long periods is the main consideration, the 

 gravity, Daniel (or telegraph) battery is largely used. Its great 

 defect of feeble current can be largely overcome by having a 

 considerable number of cells controlled by a cell-arranger. Thus 

 a battery of 20 cells, which can give at most but 1-5 ampere 

 with the ordinary series arrangement, may give nearly 20 times 

 as much by use of the cell-arranger. 



It is a very great advantage to the overworked teacher or 

 investigator if he is able, by a little more labor at the outset, 

 — say in vacation time — to have an apparatus so easily managed 

 that he. may, at a moment's notice, always have his battery 

 properly arranged for a new duty. I suppose it is due to the 

 considerable labor of changing connections in an ordinary bat- 

 tery that so general a disregard and even ignorance, of the simple 

 principles of best action in a battery prevails. I should judge 

 that such an arrangement would be especially valuable in the 

 study of nerve stimulation as it gives such ready control of the 

 voltages applied. I can testify particularly to its convenience 

 in different kinds of electrical testing. 



But all of the batteries thus far considered fail in this re- 

 spect ; their electrical properties do not remain constant. We can 

 not be sure that we can exactly reproduce the result today which 



