1878.] 



Sir W. Thomson. Harmonic Analyzer. 



373 



f 2irwX -, -, f • 27TIVX-, 



\y cos dx, and \y sm ax ; 



where u denotes the angular, velocity of the shaft carrying the second 

 pair of shafts, that of the first being unity. 



The machine, with the toothed wheels actually mounted on it when 

 shown to the Royal Society, gave iv = 2, and was therefore adopted for 

 the meteorological application. By removal ot two of the wheels 

 and substitution of two others, which were laid on the table of the 



39 x 109 



Roval Society, the value of u> becomes -* (according to 



J J ' 40x110 v 



factors found by Mr. E. Roberts, and supplied by him to the author, 

 for the ratio of the mean lunar to the mean solar periods relatively to 

 the earth's rotation). Thus, the same machine can serve for analysing 

 out simultaneously the mean lunar and mean solar semi-diurnal tides 

 from a tide-gauge curve. But the dimensions of the actual machine 

 do not allow range enough of motion for the majority of tide-gauge 

 carves, and they are perfectly sufficient and suitable for raeterological 

 work. The machine, with the train giving iv=2, is therefore handed 

 over to the Meteorological Office to be brought immediately into prac- 

 tical work by Mr. Scott (as soon as a brass cylinder of proper dia- 

 meter to suit the 24A length of his curves is substituted for the 

 wooden model cylinder in the machine as shown to the Royal Society) : 

 and the construction of a new machine for the tidal analysis, to have 

 eleven disk globe and cylinder integrators in line, and nine crank 

 shafts having their axes in line with the paper drum, according to the 

 preceding description, in proper periods to analyse a tide curve by one 

 process for mean level, and for the two components of each of the five 

 chief tidal constituents — that is to say, 



(1.) The mean solar semi-diurnal ; 



(2.) „ „ lunar 



(3.) ,, ,, lunar quarter diurnal, shallow water tide ; 



(4.) ,, ,, lunar declinational diurnal ; 



(5.) ,, ,, lum-solar declinational diurnal ; 

 is to be immediately commenced. It is hoped that it may be com- 

 pleted without need to apply for any addition to the grant already 

 made by the Royal Society for harmonic analysers. 



Counterpoises are applied to the crank shafts to fulfil the condition 

 that gravity on cranks, and sliding pieces, and sectors, is in equilibrium. 

 Error from " back lash " or " lost time " is thus prevented simply by 

 frictional resistance against the rotation of the uniformly rotating 

 disk and of the tertiary shafts, and by the weights of the sectors 

 attached to the oscillating disks. 



* The actual numbers of the teeth in the two pairs of wheels constituting the 

 train are 78 : 80 and 109 : 110. 



