OF REICHERT's H.EMOMETER. 15 



common, absolutely level surface. Only in this case does the 

 partition wall appear in the projection as a parallel limited black 

 stripe, of a thickness corresponding . to that of the partition wall. 

 If the hquid in either half, or in both halves, has a meniscus 

 (positive or negative), the dividing line appears distorted, widened 

 in the centre or at both ends, cut by fine glistening white lines, 

 also widened and following the line of the rim in several bands. 

 In a similar manner a coloured field, covered by a meniscus, semi- 

 circular in the interior, and a distortion of the boundary with a 

 contraction of the coloured surface brought forward for comparison 

 is discovered ; although in a lesser degree, this is nevertheless still 

 perceptible just as is the distortion which the picture of the 

 partition wall suffers in consequence of a meniscus. This also 

 affects the exactness and the reliability of the final result. The 

 simplest method of avoiding this defect arising from the presence 

 of the meniscus, is to bestow the requisite amount of attention 

 and care in procuring a perfectly level surface of the fluids in each 

 half of the vessel. Although this task may be disagreeable, it 

 should not be called difficult, since circumstances permit an 

 approach to this end from both sides, and also since the trans- 

 gression of the proper limit does no great injury. This of course 

 is obvious in regard to the wedge half; for the blood half the 

 same holds good according to what has already been said. 

 Proceed with the same care in case withdrawal of the surplus 

 liquid is necessary from the blood half. That is needed in adding 

 the last portion of water to this half, as every current may lead to 

 a mixing of the upper and lower layers of water. This surplus of 

 water may be removed either by means of thin glass capillaries 

 or by filtering paper. In either case avoid dipping too deep into 

 the water. The wetting and overflowing of the partition wall may 

 be avoided, when this edge has been greased beforehand. 



A second method of eliminating the meniscus presupposes 

 the fulfilment of the instructions given above. This method 

 provides purposely a distinct meniscus for each half, or in case of 

 the overflowing of the partition wall, which is here very probable, 

 fills it until the whole surface forms a convex meniscus. Then 

 place a small cover-glass over the opening of the vessel that no air 

 bubble may be inclosed and without allowing the upper side of 



