During these journeys he discovered the connection between the Amazon and Orinoco river systems and surmised that altitude sickness was caused by lack of oxygen. 旅程中他發現亞馬遜河系與奧利諾科河系是相通的，並推測高山病起因於缺氧。
For many, approaching Tibet gradually by train will be preferable to flying in, as it will allow more time to acclimatise and reduce the chance of altitude sickness. 更好的是，與坐飛機相比，乘火車將是逐漸的抵達西藏，這樣將使乘客有更多的適應時間和降低發生高山病的幾率。
