476 Dr. Tycho E :son Auren on the 



is furnished with two additional pipes, one in the lower and 

 the other in the upper part of it. By means of a short 

 tubing the lower one is connected with a vessel containing 

 the liquid to be examined. The other pipe is applied for the 

 purpose of sucking up the liquid into the vessel. The other 

 absorption vessel, that in what follows is designated as the 

 comparator (F), consists of two parallel brass laminse, pro- 

 vided with round apertures (3 cm. diam.), covered with thin 

 mica, and the borders of these laminse are connected by 

 rubber cloth so that a water-tight bag is obtained. To the front 

 lamina is applied an additional tube (Gr), that communicates 

 by a rubber tube with a water-cistern, from which the vessel 

 is supplied with water. The two brass laminae are firmly fixed 

 in a dividing machine (M), so that by the aid of the screw 

 of the machine they may be caused to slide on each other, 

 and so the thickness of the water be changed, and this change 

 be accurately determined. The bulb, consisting of a Siemens 

 tungsten tube with fin radiator for cooling the an ticathode, 

 through which passes a current of O'5-l milliampere, is placed 

 in a box (I), coated with lead, and furnished with two apertures 

 directly in front of the two absorption vessels. For the pur- 

 pose of filtering, an aluminium screen (H) 1*25 mm. thick is 

 applied. The ionization-chambers are charged up to -f 220 

 and —220 volts respectively, and the electrodes in them 

 are connected with each other as well as with a string- 

 electrometer (K) of Lutz-Edelmann, in which there is a 

 Pt-string of 0*001 mm. thickness. The sensibility of the 

 electrometer amounted to about 1 volt for one division of 

 the scale. All the conductors are protected by metal tubes, 

 which are earthed (J), and the electrometer-string (S) also, 

 by means of a simple key (L), can be earthed. As current 

 source for the bulb, I have used a high-tension transformer 

 of Siemens' construction. 



The determinations were carried out in the following 

 manner. The absorption vessel is first filled with water, 

 whereupon this, as well as the water-filled comparator, was 

 exposed to radiation. The electrometer-string having been 

 momentarily earthed, it is observed to which side the string 

 seems to be moving. By augmenting or diminishing the 

 thickness of the water-sheet in the comparator, radiation in 

 the two ionization-chambers can be made to be equal in 

 strength, in which case the currents neutralize each other, 

 and the electrometer-string will remain at rest. The position 

 of the screw (d\) is read, whereupon the water of the 

 absorption vessel is exchanged for the solution whose ab- 

 sorption coefficient has to be determined, the comparator is 



