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been placed hia'her than these connection-canals so as to make it 

 more difficult for the mercury to get into them. The footplates of 

 the stopcocks are fastened by means of wood-screws on the stopcock- 

 board. The connection of the stopcocks with the steel T-pieces is 

 obtained again by marine-glue fastened by soldering-work ; al those 

 parts and the coupling by nuts and taps proved perfectly reliable. 

 After the manometertubes have been coiuiected, the whole apparatus 

 is exhausted through the stopcock Kq (at the same time coupling 

 the left side of A to the airpump) and is filled with gas from the 

 main feeding tube. 



When there are still leakages in the apparatus after this has been 

 performed, these are shown by the motion of the mercury columns 

 when the manometer is brought to pressure. They are then detected 

 by passing a pencil with soap-water or oil along the suspected 

 seams, and generally they can easily be repaired without removing 

 any of the separate manometers from the apparatus (which however 

 would not offer the least difficulty owing to the elasticity of the 

 glass capillaries, the flexibility of the steel capillaries, the mobility 

 of the boards and the suitable position of the joints). 



7. Corrections. In computing the pressure from the read height 

 of the mercury the ordinary corrections for open manometers must 

 be applied. 



I need not dwell upon the well-known small corrections which 

 the theodolite-readings (conip. § 5) might require, from the telescope 

 being not perfectly level in the way of reading which is followed 

 here; I will only suggest that the correction for the capillarity may 

 be applied by determining the height of the meniscus by means of 

 the reading telescope. We have however not yet much experience 

 about that correction and till now we tried to equalize the two 

 menisci in one and the same tube as much as possible by knocking. 

 There are however two corrections resulting from the peculiar con- 

 struction of the apparatus on which I shall have to make a few 

 remarks. 



The first correction is that for the difference of pressure in the 

 compressed gas near the lower meiiiscus in the one and near the 

 upper meniscus of the next manometertube. If the corrections must 

 be very small we might use for the supply of pressure compressed 

 hydrogen, this may be of advantage for very high pressure, at GO 

 atmospheres or 45600 m.m. the correction for all hydrogen columns 

 together is not more than about 9 m.m., at 100 atm. or 7G000 m.m. 

 not more than 21 m.m. so that these corrections have only to be 

 applied to measurements, which are very accurate. But as the slightest 



