24 Incompleteness of our present knowledge. 



Are the " elementary substances " really compound 

 bodies ? Are they all compounds of Hydrogen ? Are 

 they all decomposed by very high temperatures, as 

 compound substances are "disassociated" by less 

 elevated temperatures ? Under what conditions is 

 Fluorine isolated ? Do gases transmit heat by 

 conduction ? Under what circumstances is Light 

 converted into Electricity ? and into Magnetism ? 

 What is the actual size of an atom of Hydrogen ? 

 Does Light (without heat) expand bodies ? What is 

 the actual molecular arrangement of the atoms of 

 Hydrogen at 60 Fahrenheit ? What is the cause of 

 the absence of metalloids in the Sun ? What are 

 the properties of Fluorine ? What is the vapour 

 density of Caesium ? Under what circumstances is 

 heat wholly converted into mechanical power ? &c., &c. 

 All these discoveries when made, will probably, 

 sooner or later, be productive of practical benefits 

 to mankind. 



Nearly ever manufacturer in this country is 

 deriving, from scientific discoveries, advantages for 

 which there has been little or no payment made to 

 the discoverers. The makers of coal-tar-dyes, and 

 dyers of wool and silk, are using Mitscher- 

 lich's discovery of nitro-benzine. Manufacturers of 

 picric acid and " French purple" have enjoyed the 

 fruits of the labours of Dr. Stenhouse. Makers of 

 chlorate of potash and cyanide of potassium are 

 profiting largely by the discoveries of Scheele, Gay- 

 Lussac, and others. All the percussion cap makers 



