We also find considerable lack of clarity in Jeans's writings. For example, at one place, stating the universe to be formed of the ethers and their undulations, he writes: "........the ethers and their undulations, the waves which form the universe, are in all probability, fictitious. This is not to say that they have no existence at all: they exist in our minds, or we should not be discussing them; and something must exist outside our minds to put this or any other concept into our minds. To this something we may temporarily assign the name 'reality,' and it is this reality which is the object of science to study. But we shall find that this reality is something very different from what the scientist of fifty years ago meant by ether, undulations and waves, so much so that, judged by his standards and speaking his language for a moment, the ethers and their waves are not realities at all. And yet they are the most real things of which we have any knowledge of experience, and so are as real as anything possibly can be for us."[1]
Now, if we examine this statement critically, we at once become aware of ambiguity therein. Firstly, Jeans calls the ethers and their undulations fictitious (in all probabilities). This would mean that there is no real existence of the ethers and their undulations, and hence, the universe which is formed by these fictitious ethers and their undulations is also fictitious. But Jeans himself concedes that 'fictitious' does not mean that they (ethers and their undulations; have no existence at all. Thus he states them "to have existence in our minds." Also, he feels that there must be something existing outside our minds' (i.e. existing objectively) which is responsible for our thinking of the ethers and their undulations. Thus if this "something" is an objective reality, how does it reconcile with Jeans's view that being formed of ethers and their undulations, the universe is fictitious (for the "something" cannot be considered to be outside the universe). Secondly, Jeans maintains that the waves and their undulations as meant today are the most real things. Then, how the universe can be considered to have no existence outside our minds? Such sort of confusion prevails everywhere in Jeans's writings. It becomes very difficult for the reader to make out what exactly Jeans wants to say.
Here also like Eddington, Jeans himself seems to be in confusion, This becomes clear from his statement[2] in which he considers it difficult to draw a line of demarcation between realism and idealism. He clearly accepts the existence of objective realities, all the same he flounders to call them "real" and designating them "mathematical", he tries to show the universe to be made up of pure thoughts. Jeans's statement that the universe consists of pure thought of a mathematical thinker[3] has, instead of rendering his view intelligible, made it more abstruse.[4] Similarly, his concept of substantiality[5] is also difficult to be comprehended.
It is interesting to note that Eddington also does not comply with this view of Jeans. Eddington comments: "I cannot accept Jeans's view that mathematical conceptions appear in physics because it deals with a universe created by a Pure Mathematician." (-The Philosophy of Physical Science, p.137).