Hakuin's writings which contain the best-known descriptions of two of the internal practices used in Japanese Rinzai Zen, the Nanso no Ho and Naikan no Ho practices used to strengthen energy and remedy imbalances, are Yasen Kanna ("Idle Talk on a Night Boat") and Orategama ("The Embossed Tea Kettle").
Here are a few translations of these which are still available. I'd be interested to see any other resources...please post them if you have them!
A good translation of the preface to Yasen Kanna, in which the naikan method is summarized, may be found in one of Shodo Harada Roshi's articles here:
http://www.onedropzendo.dk/nyhedsbreve/nr_80_jun09.pdf
For those with access to JSTOR, an older translation of Yasen Kanna is here:
http://www.jstor.org/discover/10.2307/2 ... 1142921043
Yampolsky's The Zen Master Hakuin contains a translation of Orategama:
http://www.amazon.com/The-Master-Hakuin ... 0231060416
Wild Ivy, Waddell's translation of Hakuin's autobiography:
http://www.amazon.com/gp/product/157062 ... B000N9FVM0
Finally, translations of both Orategama and Yasen Kanna be found in this volume which has been posted online (pdf):
http://www.naturalthinker.net/trl/texts ... Kettle.pdf

