4 1 20 On preserving the Balance 



glass, the whole being set in a stout framework of zinc, and cemented 

 with what is known under the name of Scott's cement, and which I 

 have found to answer for the purpose most admirably. Within this 

 tank were arranged several large pieces of rock-work, thrown into an 

 arched form, and other fragments were cemented in places against the 

 slate at the back and ends, and at parts along the water-line, so that 

 the creatures could hide themselves at pleasure ; a short beach of 

 pebbles was also constructed in order that shallow water could be re- 

 sorted to if desired. The whole tank was covered with a light glass 

 shade to keep out the dust and retard evaporation. 



With the sea water obtained in January, 1852, 1 have been working 

 without cessation up to the present time, agitating and aerating when 

 it became foul during the unsuccessful experiments on the sea-weeds, 

 but since then it has been rarely ever disturbed ; the loss which takes 

 place from evaporation being made up, as before stated, with rain or 

 distilled water. 



For a considerable period, after commencing these experiments, 

 I was much troubled to obtain living subjects in a healthy condition, 

 but having alluded to this, and the success of my investigations, 

 in a short notice appended to a paper published in the ' Annals ' for 

 October, 1852 (see also Zool. 3633), my friend, Mr. P. H. Gosse, 

 who was then sojourning at Ilfracombe for his health, offered in the 

 kindest manner possible to supply me with materials, and from that 

 period he has always most heartily responded to my wants. It must 

 not be imagined for a moment that the beautiful creatures I have thus 

 received have been all preserved alive or always quite healthy. In 

 experimental investigations this would be unreasonable to expect, as 

 the very fact of experimenting implies a disturbance of the then state 

 of things. Besides which, from want of a sufficient knowledge of 

 Natural History, from want of forethought and experience and other 

 causes, I have lost many very fine specimens ; and as the detail 

 of these losses may prevent the occurrence of the like annoyances to 

 others, I shall venture to occupy your time for a short period with 

 their history. 



My greatest loss arose from too great an anxiety to transfer the col- 

 lection I had preserved in a healthy condition to the end of December, 

 1852, into the new tank. As soon as it arrived from the maker's I lost 

 no time in introducing my numerous family to their new abode, and 

 dearly I paid for my precipitancy, for on the next morning I found 

 many of my most beautiful specimens dead ; thus 1 lost two fine 

 Holothurias (//. Pentactes), a small freckled goby (Gobius minutus), 



