30 EEPORT 1880. 



insulation is required they are pulled out so as to leave the conductors free 

 of the holes, touching nothing. 



To each of one pair of brass caps a short brass pin is attached, the 

 two projecting horizontally one above the other. To the other pair two 

 brass or bronze flat springs are screwed, which project between the two 

 pins attached to the other pair of caps. Except when depressed the 

 springs both press upon the upper of the two pins and make contact with 

 it. AH the contact surfaces are gilt. Either spring can be depressed 

 separately without bringing the hand near it, by means of a thin g-lass 

 rod, which works through a hole in the top of the case, and which is 

 shod with metal above and below, so that it may not be subject to any 

 friction which might electrify it. 



The piece of metal at the top is a brass cap sliding over a tube fixed in 

 the top of the case in such a way as to exclude dust ; it can be pressed 

 down with the fingers, and is sent up again by a spiral spring. A pin 

 and double bayonet-slot is also arranged so as to fix the piece perma- 

 nently in either of three positions, viz., completely up and in contact 

 with the top pin, completely down and in contact with the bottom pin, 

 half-way or insulated. 



In its present form the key is in principle simply an ordinary double 

 reversing key turned upside down and shut up in a box. 



The glass pillars are fixed to the lid instead of to the floor of the case 

 for several reasons, one of which is that it economises space and reduces 

 the height of the key. The lid can be unscrewed and taken out of the 

 case with all the working parts in situ, which is very convenient. The 

 floor of the case is quite free and can be removed at pleasure. A dish 

 stands on it to contain pumice soaked with sulphuric acid whenever 

 extra insulation is required. Without any artificial drying, however, the 

 insulation is very good. The dish is made either of lead, or of glass pro- 

 tected from the working parts by a covering of wire gauze. 



The key has been made by Elliott Bros, in two forms — one square, the 

 other round. The round form of case is distinctly the cheaper ; it 

 necessitates a slight modification in the arrangement of the working 

 parts, but it appears to be nearly as convenient as the other. 



Report of the Committee, consisting of Professor Cayley, F.R.S.y 

 Professor Gr. Gr. Stokes, F.R.S., Professor H. J, S. Smith, F.R.S.^ 

 Professor Sir William Thomson, F.R.S., Mr. James Glaisher, 

 F.R.S., and Mr. J. W. L. GtLAISHER, F.R.S. (Secretary), on Ma- 

 thematical Tables. Drawn up by Mr. J. W. L. GtLAIsher. 



The present Report relates to the factor tables for the fourth, fifth, and sixth 

 millions, and to some results of the enumeration of the primes in the 

 fifth million and the first five millions. In Section I. an account is given 

 of the state of the work, two volumes of which have been pubUshed, 

 while a portion of the third and concluding volume is already in type. 

 Section II. contains in a condensed form results relating to the distribu- 

 tion of primes in the fifth million, obtained by enumerating the primes in 



