8 



HARDWICKE'S SCIENCE-G OSSIF. 



Canada balsam, thus prepared, may be very various- 

 ly applied ; but other methods are modifications 

 rather than essentially distinct from the processes 

 described above. I hope in future papers to treat 

 explicitly of some of these. In every case I shall 

 make it a rule to explain only zvhat I have verified by 

 repeated experiment, so that these notes may be of 

 essentially practical utility to my readers. 



A NEW AQUARIUM. 



ONE of the chief drawbacks to private marine 

 aquaria, or hatching tanks, is the elaborate and 

 costly machinery necessary to aerate the water : and 

 even when such aeration is, or may be, carried on by 



Fig. 4. — A, Series of hatching tanVs ; B, two' dark reservoirs working by a 

 rope over c ; c, a wheel ; D, hooks to hold up the full reservoirs : E, over- 

 flow pipe from bottom tank to the empty reservoir ; f, flexible joints to E ; 

 G, hole in reservoir in which overflow pipe slides easily. 



a gentle circulation, promoted by a fall of water from 

 a higher level, the labour of getting the water to 

 such higher level constantly, is a source of trouble, 

 and therefore soon left undone, to the destruction of 

 the living contents of the tank. 



In the annexed sketch I have given an idea for 

 producing a flow of water through a series of shallow 

 tanks, which may be adapted to a small or large 

 undertaking as desired. The principle is, that 

 whilst one reservoir is discharging its contents into 

 the top tank, the bottom tank is overflowing into 

 the other, which, when full, can by a contrivance so 

 simple that I have not thought it necessary to show 

 it in the sketch, be pulled up to discharge its con- 

 tents, in turn, into the top tank. 



Now we will suppose that the reservoirs have a 

 capacity of five gals., and that the full one has been 

 hauled up to its position and secured there. By 

 turning on the tap, which must of course be on 

 flexible joints to prevent fouling the edge of the tank 

 in its descent, a small stream of water will fall into 

 the top tank, and overflow into the next and so on, 



till it reaches the empty reservoir. When the upper 

 reservoir is empty the lower one is full, the circula- 

 tion ceases, and therefore no waste of water takes 

 place. 



When the time occupied by the discharge of the 

 full reservoir is known, it is a very simple matter for 

 anyone near the tank room to go at stated intervals 

 and reverse the gear, an operation occupying about 

 half a minute. 



Of course if the tanks be wide ones, two wheels, 

 at a corresponding width apart, will be necessary. 

 The advantages of this plan are as follows : — 

 Its comparative cheapness of material. 

 The ease and rapidity with which the level of the 

 reserve tank can be altered. 



That a certain quantity of water is always in the 

 dark, and therefore the "dark reservoir" 

 is thus obtained. 



That when the reservoirs are large, and 

 the stream small, thus occupying some 

 time to discharge, an almost constant 

 stream can be maintained if some one 

 near at hand can be relied upon to 

 devote 30 seconds, say four times a day, to 

 reversing the gear. 



That it is not likely to get out of order, 

 if well made in the first place. 



I shall be very pleased to give anyone 

 desiring it, any further information, and I 

 feel sure that this simple and labour-saving 

 method will commend itself to those who 

 wish to keep a marine tank or study the 

 minute organisms of the sea in their 

 metamorphoses. 



I may mention that the tanks should 

 be covered with sheets of glass to keep 

 off dust, but having a round hole for the 

 overflow water to drop through. A series of tanks 

 like this, rigged up in a cool room, say an out-house 

 for instance, will, with care, do wonders. 



Edward Lovett. 



Croydon. 



A GROWING-CELL FOR MINUTE 

 ORGANISMS. 



THE number and variety of " growing-cells " from 

 which microscopical workers may choose is 

 large, but it now seems necessary to increase it by one 

 more. Desiring a slide of the kind for the study of 

 minute animal organisms, capaljle of use with im- 

 mersion objectives, I have hit upon the] following 

 arrangements, which I hope the microscopical readers 

 of Science-Gossip will find as useful as I have. 



The materials needed to build this little device are 

 an ordinary slip, a thin cover I inch or less in 

 diameter, two glass rings, a thin square, and a drop 

 or two of Canada balsam. Every microscopist has 



