4960 The Aquarium. 



they are given as they occur to memory, or as notes were made 

 at the time. 



George Guyon. 

 Ventnor, Isle of Wight, 

 November 20,1855. 



On the Injurious Effects of an Excess or Want of Heat and Light on the 

 Aquarium. — Temperature is a point requiring great attention in carrying out success- 

 fully the principles of a permanent aquarium. The mean temperature of the ocean is 

 estimated to be about 56° Fahr.,and this, under ordinary circumstances, does not vary 

 more than about 12° throughout the different seasons of the year. The causes of this 

 equilibrium will be readily understood when we take into consideration the effects that 

 must be produced by the continued flux and reflux of the tides, and by the enormous 

 streams of water which must be flowing from the Arctic regions from year's end to 

 year's end in one constant current, and which, by their movement, must necessarily 

 cause other currents to flow in and take their place, thus forcing, as it were, the heated 

 surface-water of the tropical seas towards the colder regions of the globe. Again, the 

 whole surface of the earth, submersed below the ocean, is protected by this fluid 

 coating from the effects of the cooling influences of radiation on the one hand, and 

 from contact with the currents of the atmosphere on the other ; and hence we perceive 

 an always existent cause for the maintenance of a steady, equable temperature by the 

 waters of the ocean throughout the year. Many of the inhabitants of the sea are very 

 sensitive to changes of temperature, and we find that a few degrees of variation will 

 cause them rapidly to move their position and seek some cooler or warmer spot, as the 

 case may be. In the ocean it will be evident that the creatures have the power readily 

 to effect this under ordinary circumstances, by seeking deeper water not liable to be 

 affected by atmospheric influences, by partially or entirely burying themselves in the 

 sand or shingle, or by shielding their bodies under the protecting shadow of the rocks 

 or growing vegetation. In arranging the rock-work in the interior of the aquarium, 

 therefore, great care should be taken to keep these points in view, and to afford as 

 much protection as possible to the creatures from the cooling influences of radiation 

 on the one hand, and from the heat of the sun's rays on the other. From my own 

 experience I find that the range of temperature should not be below 50° Fahr., nor 

 above 70° ; within these limits all appears to progress healthily, but beyond these 

 points many of the creatures are rapidly affected. During the last long-continued and 

 severe winter, it was found very difficult, in an ordinary sitting-room having a south 

 aspect and a good fire maintained throughout the day — the tanks being also screened 

 at night by a blind — to prevent the powerful cooling effects from radiation on a clear 

 frosty night; and on three several occasions, marking exactly the three severest frosts 

 that we experienced during the winter, the thermometer, immersed in an aquarium 

 containing about thirty gallons of water, fell as low as 45° Fahr. The shrimp and 

 crab tribes, and the Crustaceans generally, are especially affected by these changes, 

 and on each of the three occasions alluded to, one or two individuals perished ; the 

 larger-sized prawns, as Palaemon serratus, appeared to suffer more readily than the 

 P. Squilla, although this might arise from the smaller ones being able to find a shelter 

 from the radiation by concealing themselves more completely among the rock-work or 

 vegetation. Anthea Cereus is also very sensitive to considerable variations of tempera- 



