68 



INVESTIGATION OF TEMPERATURES. 



It was intended that a self- registering thermometer should be placed on each hurdle, and that 

 the temperature to which the young were exposed should be noted at each examination. Fortu- 

 nately, considering the fate of the hurdles, the thermometers were not received in time to be used 

 as was intended, and after the disappearance of the spat collectors it was not considered advisable 

 to expose the thermometers to the same risks.. About the last of July, however, I had the tem- 

 perature of the surface water recorded every two hours, and considering that there is probably 

 but little variation in the limits of the Sounds, I have plotted the accompanying curve of maxi- 

 mum and minimum temperatures from July 29 to October 1. It will be seen that these curves are 

 very irregular, and that the greatest irregularities occur during the month of August, and that 

 the greatest difference is between the 6th and 10th of August, one of 15° in four days. On the 

 15th there is a change of 8°, and on the 28th of 12°._ 



About the 4th of August I determined to utilize the channel buoys as marks for the positions 

 of thermometers, hoping that they might thus escape the observation of those who were inclined 

 to remove them. Accordingly, we placed four self- registering thermometers on the beds ; one at the 

 foot of the buoy on the Shark's Fin, one on the buoy on Piney Island Bar, one on the buoy off 

 Watts' Island light-house, and one on the buoy off Syke's Island, about the middle of Pocomoke 

 Sound. We were enabled to make several examinations of these thermometers; but about the 

 1st of September, finding that one had been stolen, I concluded to remove the others before they 

 shared the same fate. 



The curves of maximum and minimum temperature given by these thermometers, and also the 

 range of variation, are shown on the same sheet with the curves of surface temperature. 



The thermometers were in place too late, and for too short a period, to allow any safe conclu- 

 sions to be based upon the information given by them; but it is noticeable, as an interesting coinci- 

 dence, that the curves of both surface and bottom temperatures show the greatest variations about 

 the time when the young were what is known as "spat," or during the period of and just before 

 attachment; the young on the shoal beds presumably attaching by early August, and those on the 

 deep water or southern beds somewhat later. I regret that it was impossible for me to more thor- 

 oughly study the effects of the change of temperature, as I think the failure or success of the 

 spatting, other things being equal, will be found to depend mainly upon the temperature to which 

 the mature oyster and embryos are exposed during the spawning season. 



INVESTIGATION OF THE CHANGES IN DENSITY OF THE WATER. 



In order to have definite information as to the change of density of the water surrounding the 

 oysters, and regarding such changes during the spatting season as of most importance, and as the 

 maximum change would be most likely to occur about the time of the spring tides, I determined 

 to obtain specimens of water on a certain number of sections across each Sound at high and low 

 water of the spring tides. The sections were located as follows, and are shown on the sketches 

 accompanying this report: 



Section No. 1 was just above Hooper's Strait and at the mouths of the Nanticoke and Wicom- 

 ico Eivers, in order that the influence of both the strait and rivers might be shown. 



Section No. 2, for the same reason, was north of Kedge's Strait and across the mouths of the 

 Manokin and Big Annemessex Eivers. 



Section No. 3 was across the entrance of both Sounds, south of Watts' Island. 



Section No. 4 was across the middle of Pocomoke Sound, that the influence of Guilford and 

 Mesongo Creeks might be known. 



Section No. 5 was above the natural beds of Pocomoke Sound and across the mouth of Poco- 

 moke Eiver. 



Stations were selected on these sections in such a manner as to obtain specimens of the water 

 that passed over the beds, and the specimens were taken by means of the drop-water cylinders at 

 every two fathoms of depth. As soon as possible after securing them they were tested with the 

 hydrometer. The results are tabulated in the " record of densities," and curves showing the various 

 changes accompany this report. All densities are reduced to a standard temperature of 60° Fahr., 

 and 1,000 represents the density of distilled water. 



